Advice on some new (old) clubs - blades for a high handicapper

How much are you willing to spend?  Re-shafting/re-gripping your current clubs could be as expensive as getting another set of irons (used or new depending on the make).  This is the time of year to find deals too - as many folks are putting away the clubs for the winter months.  And a lot of retailers are discounting clubs to make room for next seasons inventories.

I'll never carry a 3 or 4i again. Now have 2 lovely Cleveland hybrids which surpass in all respects those irons.  Very rarely do i wish for the 4 iron and that is  only  when i am under the bush and need to hack it out but otherwise both are left at home.  If you have not tried various hybrids lately  i suggest that you do so before you spend your money or condemn the set, 5-PW,  without those irons.  I am speaking to your age, current golf status and ability.  

There's a school of thought that says a higher handicap player can benefit from playing blades.  They're much less forgiving and therefore, force the player to develop a much better, more consistent swing.

I am NOT of that school.  Golf is supposed to be fun.  Irons that provide a degree of game improvement, with a bigger sweet spot and the ability to help get the ball in the air are going to make it that much more fun for the average player who doesn't play more than 50 rounds a year and practices infrequently.  If you're looking to play and enjoy it NOW, I'd recommend looking at such a club, or as you said, simply reshafting your Mizunos if you're otherwise happy with them. 

If you want a forged iron, there are plenty out there that offer a cavity back and game improvement features.  I'd also offer that most people wouldn't be able to tell the difference in hitting a modern cast iron vs a forged iron.....but that's a different discussion.