The mentioned
HPL kit is very worth it in my opinion. I swapped a
system's worth last year and might do more. Cleaned and painted the bodies at the same time, added strain reliefs. My 6" fresnels are a mix of various generations going back to some ancient Century fixtures and just a few Altmans. Maybe for that reason or maybe just due to the slightly wacky construction of the whole retrofit kit, it wasn't quite as smooth a swap as one might hope, but with a little tinkering they all went together. The spot/flood sled (is that an official term?) doesn't slide nearly as easily as the original equipment, and I think has less available travel than before, but since I usually keep them near center of travel anyway it doesn't bother me.
A cheaper solution, especially if you have a large
stock of medium
prefocus lamps to burn through before making the
switch, is to get a Dremel and a couple different shaped grinding stones and clean up the surface of the contact in each cruddy lamp
base. Several people on CB do this, including me, and you'll find a thread or two if you search. Also flood the spring area of the contact with contact cleaner and move it around until the spring works again, since those often start to stick too far down making the arcing worse too. You can clean up the "BB" on the bottom of a lamp with some fine sandpaper too, but if it is too far gone you're better off throwing it out because it will just make the freshly surfaced
socket arc and heat up faster. The more you re-surface, the shorter they last before needing it again, and eventually you remove too much material to put them back in service, so it still isn't ideal. If you have the money now to retrofit full systems at once, and don't have lots of
MPF lamps that would be wasted, jump right to the
HPL kit.
I know I'm not the only one who has a deep resentment of
PARNel inventories. Not
ETC's finest achievement. The beam and
gel life stinks in comparison to a true
fresnel, and the focusing mechanisms are prone to failure. Stick with the real thing, or get S4 PARs if you want new fixtures.