For me it was a case that I just couldn't seem to shoot any lower on my handicap, driving passable, putting above average but even though I was hitting the ball well, I just seemed to be leaving myself too much to do.... Got down to 80 and then pretty much shot that score every round plus or minus a couple of shots. ( game improvment clubs brosnans gradys, pgf v8's and tommy 855's)
Didn't have alot in the way of money so went to a place that had heaps of sets of second hand clubs, went out and hit them all I think and ended up purchasing a set of wilson staff proggressives (proggresive blades).... was nearly not going to have a hit with them as they have small heads and my thoughts were, these will be harsh to hit, to unforgiving, long story short they felt like hitting the ball like butter and were extreamly straight. Also I found the distances very consistent.
So from my experience, you will know when you need an upgrade and need something specific, also, try heaps of different types and see what you like.