the guys have covered the TS9/TS808 differences etc, there's more info here:
http://www.analogman.com/tshist.htmWhile the chips make a difference, i don't think they make anything like as much difference as corksniffers reckon they do, i think the vintage JRC4558D thing is a way to justify charging more money. the variations of the 4558 chip are all pretty good, vintage or not.
The Keeley pedal tubescreamer.. well.. my opinion on it may be coloured as i was lucky enough to get a vintage chipped true bypass, mod plus one off the bay a few years back for what turned out to be a total steal compared to what they go for new, so am guessing the prices new were not even remotely close a few years back.
Anyways.. i digress. the Keeley (and analogman silver mod) both tighten up the low end (previously flabby) gets rid of the mid range hump (there is still a pronounced midrange as that's what a TS sounds like, but makes it less nasal and honky), gives you more range on the gain knob (at the lower end it's way way cleaner and at the top end there's more gain available), makes the pedal true bypass, and generally upgrades a lot of components for higher quality ones so you get less noise.
The fuss is that these companies are very good at marketing, and while they do improve these pedals in some cases considerably, I am just starting to not be convinced by how expensive the prices are starting to become:
http://www.guitarguitar.co.uk/pedals_s_detail.asp?stock=06061010482429to put that into context i got mine for about 130 quid used on the bay with a vintage JRC (as i mentioned) . There's corksniffers out there would and have literally creamed their pants and offer me stupid money for it. not that i would get rid of it. To be honest if i was going to spend that money on a pedal i would buy an analogman KOT, or the tubedriver. If i wanted a modded TS808 now i would get in touch with these guys.
http://www.pedalmods.com/and if i wanted a TS9 or TS 808 i would but an old one of the bay from the 90's or early 2000's
Just saw the prices of the current ibanez reissues, so i take back what i said about Keeley's prices, they only cost £40 more than the base price of the basic pedal.. I can't believe how expensive the ibanez reissues have got. It's less of a question of whether the mods are worth it and more a question of is a tubescreamer worth it. I would say no, there's better pedals for less money.