Afraid I don't have much to contribute joystick-wise, but as far as the hardware:

Personally, I'd shoot for a PCI Powermac of some description. The Nubus machines have limited upgrade and expansion options, and really weren't much faster compared to the 68k systems. I don't have any empirical data, but I imagine they'd chug pretty badly on Quake.
The iMacs, especially the early ones, have several issues that crop up with age (flybacks dying, speaker foam turning to goo, lack of optical drive replacements on the slot loaders), plus as you say you miss out on ADB, not to mention SCSI.

With a 7300/7500/7600, you can drop in a G3 or G4 card, stuff a ton of RAM in it, have access to both ADB on the mobo and USB with a PCI card, add a PCI Rage 128 or Radeon Mac Edition, and still have a slot left over for a SCSI card, 100meg Ethernet, Firewire, Voodoo 1/2 (which don't need a special Mac ROM), or anything you want. Or, if you're willing to shell out for one you could get a Power Mac 9600 and have room for all of the above, plus a ton of drives.
Just avoid the x200 series (slow CPU soldered to the motherboard, picky about RAM), and anything in the Spindler case (Q850, 8200, 8500, 9500 - a pain to work on, and the plastic splinters if you so much as look at it funny).
Another option is the Blue & White G3, the last desktop Mac to have an ADB port. Just make sure to get one with a Revision B motherboard, as earlier ones had problems with the IDE controller.

I lost a tray-loader iMac to a burst prom battery.

Yeah, you gotta watch those, if they go the logic board is usually a write-off.
The Maxell (red and silver) ones especially are time bombs. First thing I do when I get a Mac is open it up and check the battery.

I think an iBook G3 or iMac G3-600mhz would be your best bet.

Get as much power as you possibly can to play even early Mac games - the old Mac machines are fairly underpowered for games in my experience. Anything that runs OS9 should be fine, probably around a G4-600+ level (Quicksilver or Mirror Drive Door - though these machines sound like jet engines), and these should be comparatively cheaper and sturdier than the earlier PowerMac, Quadra and Mac II machines.

Thank you for your recommendations so far. Can anyone shed light on ADB vs. USB in regard to X-Wing and TIE Fighter? I know they both predate InputSprockets and I read somewhere else on this forum that someone who tried the same had insurmountable (not game-breaking, just less than ideal) issues trying them with a Sidewinder 3D Pro in ADB.

How far back can a late 1990s Mac go, games-wise? Can it run stuff software for the earliest Macs?

Comedy option of 2002 or 2003 eMac? 700MHz to 1GHz G4, Nvidia GF2MX or Radeon 7500, free or cheap if you find one locally as not even Mac enthusiasts seem to want them. I'm not sure about the ADB vs USB issue - I always played witth keyboard and mouse.

These are pertinent testimonies I've come across:

http://www.insidemacgames.com/forum/index.php … pic=19447&st=20

https://discussions.apple.com/thread/1563933

NamelessPlayer has several posts on his own endeavors here in VOGONS (long topics, putting "ADB" in the search box is recommended). He seems to indicate pre-InputSprockets games supported certain ADB joysticks directly (Thrustmaster HOTAS confirmed, CH also seems likely; by the way, I'm not interested in a full HOTAS since X-Wing and TIE Fighter are not that complex) and in such a mode were not actually emulating a mouse and/or keyboard. Whether that remains the case for an ADB device over an ADB-to-USB adapter (with proper drivers) or USB device utilizing USB Overdrive or some equivalent is still unclear.