I would say it depends on what club you're talking about.
For drivers I would say that the best performing drivers of all time have been made within the last five years. Aerodynamics, material science, and the proliferation of launch monitors and data driven design have resulted in improvements across the board in distance and forgiveness as of late. I know that I personally saw a decent improvement on my G10 when I switched to a G30, in that I gained between 10 and 15 yards without sacrificing accuracy. This is on the high end of what aerodynamics can provide though, simply because higher swing speeds receive a greater benefit from decreased drag. Depending on the individual you may not see much difference so long as the driver itself was made within the last ten years or so.
For irons I would be inclined to say that the main difference in the irons of yesteryear and the irons of today is forgiveness. The irons made today are much easier to hit than previous irons, simply because they aren't as drastically punishing on mis-hits as the old blades. The PING Eye2 irons seemed to be the first "widespread" GI iron that sparked the trend towards irons that were easier for the layman to hit. That being said, I found my s55 irons (their "blade" from several years ago) to be more forgiving than the Eye2's. Based on that and observations from other clubs I have hit I would say the average golfer would be best suited by irons made within the last 10 to 15 years that are in good condition with sharp grooves. If you play muscleback irons though, there's pretty much zero difference between modern "true" musclebacks and those of yore, though the current muscle-cavity irons (like the iBlade and MP-15) will likely be at least a bit easier to hit than the older blades while maintaining a similar style.
Wedges are the only thing that I would argue the "latest and greatest" provides a tangible benefit for. The reasoning for this is entirely different however, in that it's based solely off the condition of the grooves in older wedges. As wedges grow old, and get used, the grooves wear to the point that there becomes a noticeable performance difference - especially when playing out of the rough. For this reason alone do I say that the average golfer (assuming they golf at least once a week during the golfing season) is best suited by wedges no older than two or three years old.
Putters are the odd man out here. I don't think it matters in the slightest when your putter was manufactured, so long as you keep a reasonable grip on it so that it doesn't slip out of your hands. I personally am a fan of the newer milled putters for the feel they provide, but it doesn't mean I couldn't probably putt nearly as well with an original Anser putter in the same style. I think the average golfer is best suited by whatever putter style and features allow them to consistently roll the ball along their target line, with no age requirement.
In summary, considering the advancement of technology, I would feel comfortable putting these "maximum age caps" on equipment for the average weekend golfer to get the most out of his/her game:
Drivers: ~10 years old or newer
Irons: ~15 years old or newer
Wedges: ~3 years old or newer
Putter: Whatever works best for you
That being said, you may still enjoy the game with any kind of equipment out there. I just think that equipment that follows these guidelines will let the average weekend golfer get about as much as they can out of their game without necessarily breaking the bank. Like @iacas said, you may find incremental improvements by purchasing the R1 over an old G5 but the question then becomes whether or not this improvement is worth the price difference. This question can only be answered by the person buying the club. It can't be denied, however, that a driver from the 1960's will be severely outclassed by the G5 and the R1, making either of them a much better choice than the 1960's driver.
Interestingly enough, I have had the desire to go the opposite way for a while now. I bought the s55's my last go around, and I'm thinking that my next set of irons will be a more "traditional" muscleback iron (since the s55 is mostly a CB), along the likes of the MP-4 irons by Mizuno. I hit the ball consistently enough that I don't care about the lack of forgiveness, and I believe that the wonderful look and feel of those irons, along with the little bit of extra vertical control (can thin it slightly to make punch shots even easier) would offset whatever I lose in forgiveness.
I know that I would most certainly never go to an iron like the AP2, the G, or the M2. The chunky look of the club (along with the offset) gets into my head nowadays and makes me feel uncomfortable standing over the ball in a manner similar to how I used to be intimidated by the look of blades at address. I would gain forgiveness, but at the price of distance and trajectory control - an unacceptable trade for me considering I value distance and trajectory control much more highly than forgiveness.
My newest clubs are pretty old. Maybe 2006? I don't really remember. The other day, just for the heck of it, I played using my old Bazooka Iron Woods. (2i-LW) Shot my normal score. Those Ironwoods are probably 15-16 years old.
I don't think at this stage of my life, that a new set would make that much difference.
My irons are from 1978, driver and woods from 2004 (same G5 as you)....at my current playing level, I don't feel like my clubs are holding my scores back. I will be updating my wedges to something designed this century in the near future but I'll probably regrip and keep playing my grandfather's old Eye irons a couple more years.
There's something to be said about being familiar with your equipment too. The control you talk about with your driver comes from hitting a lot of balls with it and getting to know how it responds to different things. That's tough to give up considering that it could take weeks to develop that relationship with a new driver...at least that helps me cure the new toy bug and keep the wallet closed. :)