i may be that Kyma user you're talking about.... when the new hardware came out SSC gave me a really good deal on pricing, so i sold my Capybara (which i had 2 additional processing cards in) and bought a Paca.
i felt my Capy with 2 cards was sufficiently powerful enough for me. while a base system is good to start with, you may feel like you need a card or two before two long, to give yourself a bit more power.
one thing the Capy has over the new hardware is the built in audio and MIDI. the DA and AD convertors on the Capy are phenomenally good... but with the Paca you have to buy an external interface just to dedicate to it. i wouldn't recommend anything less than an Apogee Duet, quality-wise.
whether or not your system will become obsolete? that's hard to say. SSC is typically pretty regular with small udpates to kyma... adding functionality and new algorithms throughout the year, but they don't often make MASSIVE updates... that's not to say it won't happen in the future... an update that wouldn't work on the Capybara... but on the other hand, there's a lifetime of exploration in the system that's already here, so if you really got into it it's likely you wouldn't run out of inspiration...
as far as Kyma itself goes... i'll admit i haven't used my system in a while... not for any fault of the system, but i've really been getting away from software as much as i can. however, lately i've been craving it a little, so i think i'll fire it up again soon.
like most synthesizers, many of the presets sound bad.. but the nice thing about kyma is you can simply replace some default audio file that they're using with your own and all the sudden the preset sounds really great.
because a large percent of kyma is processing audio i've found that it really depends what sound your'e feeding it in order to get the best out of a patch... i've created patches that are so amazing with one sound and dont' work at all with another.
the thing i've found with kyma is that it's really easy to do quite a bit at first, which is nice... but takes a long time do master.. after many years i've hardly felt like a master at it... but i've also got inspiring sounds and processes out of it that have been huge important parts of my music.
kyma desperately needs a GUI facelift. the Tekton font and graphics they use on the slider/button interface looks horribly outdated... and probably the only area max/msp blows kyma out of the water.
kyma is a heavy system.. and it's good that you've tried it already...
i'm curious what you didn't like about it?
in terms of kyma having good reverbs.. it's true.. but you can buy some pretty killer AU/vst reverbs out there for a lot less money.... but, if you consider the fact that kyma can trivially take a reverb, split the reverb tail into 3 frequency bands, send the high frequencies of the tail through a grain stream, the mid frequencies through a delay and the low frequencies pitch shifted 4 octaves up and then reversed through another reverb..... well, you get the idea.....
(ooh, now i want to go program this...)
feel free to ask any questions you may have..