From your replies, I think I'll be looking into upgrading the box: although I guess what Kremmit said is true (the comp can always be swapped at a later date) I'd hate to waste time trying to get that old system running correctly only to ditch it. Thanks for the pointers on cheap parts - I'm sure that'll come in handy later.
My advice would still be to put an old version of MAME on the current box and see how it does with one of the tougher game you would want to play. If it does fine, then you are money ahead. If it won't do what you want, you know that before you bother setting everything up only to have to reconfigure when you go to a newer MAME on a faster box.
Are most people just eating the cost of shipping, or are they getting their parts through another vendor (or BYOACer in the BST forum) that gets them in bulk from Happ? Who are the major, reputable and most cost-friendly suppliers available?
RandyT at Groovygamegear and Andy at Ultimarc (as long as they're blue) sell a line of buttons and joysticks, but they are not true Happ parts.
If you want true Happ parts, you will save money buying from a re-seller.
Bob Roberts -
http://homearcade.org/BBBB/ http://wiki.arcadecontrols.com/wiki/The_Real_Bob_Roberts has been helping people here out since before I joined the scene.
Other respected sellers include Ponyboy, Divemaster (both on BYOAC), and TornadoTerry on E-bay.
is there a difference in the "feel" of the buttons? Does one tend to be tighter/more responsive than the other?
Leaf buttons were used in classic games - Joust, Defender, Donkey Kong, Asteroids. Generally, they have a lighter feel and faster response than micros. However, most fighters had micros, so if that is what you are going for, you will likely be fine with them. (And the micros work fine with the classic games, unless you're a purist - i.e. if you don't remember the leaf buttons, you won't miss them.) (Until you play on a real machine with them (j/k))

Joysticks are more of a concern: microswitch vs. leaf vs. optical. Does anyone know what type of stick was used in the SF type cabs?
I am guessing either Happ Supers or P360's, but I'm not a fighter guy (classics for me).
Supers and P360's have a flowing circular motion, Comps have a square restrictor so you can feel the diagonals. I think Capcom used Supers and MK used Comps, but don't know.
I'm looking for something that's responsive, but not with a tiny range of motion.
The bad thing is that will eliminate the best sticks for classic 4-way games (Donkey Kong, Pac-Man) unless you put on a dedicated stick for these. Avoid the Omni-Stick, Prodigy, Euro-Stick, Suzo 500, Mag-Stick, T-Stick, etc. if you want a large range of motion. Happ is better for this.
Do the restrictor plates on micro sticks have that 'stuck in a corner' problem?
See previous comments.
I like the idea of optical sticks, but feel they may be overkill for my needs (not to mention pricey).
Agreed. The GGG 49-Ways and the Ultimarc Universal 360's would be other options at the pricey/overkill end of the spectrum.
Happ competition seem to be a favorite (or was that ultimates? Have to check the notes...) Suggestions?
Wasn't Ultimates, very few people recommend them.