I have both phones in my hand now. The N97 keys are not raised up more than the N900 but the keyboard is more recessed so it gives a bit more travel (its a bit like using the old laptop keyboards they just felt weird unless you only used that) Overall I would say they are set about the same level from the phone. Possibly the curve makes it feel like this

Overall im not sure why I prefer the N900 keyboard (you are right their shouldn't be any difference tactually speaking). The N900 buttons are curved so when their travel ends they impact more at a point on your thumb rather than the whole area so it feels more pronounced. They are also more stiffer. Quite often I would have to stop with the N97 and check that the last key press actually went though (for some reason I don't touch type with phones) Maybe its the click sound from the OS as but tactally speaking the whole keyboard experiance on the N900 is better than my N97.

I don't dislike the layout on the N97 or the spacing. For some reason I always ended up hitting H as well as Y or R as well as T. Again this is probably because the buttons are extremely loose and easy to press so I think the fault is the keyboard is a bit too easy. I like a nice tactile response which is why I don't get on with touch-screen keyboards.

I will agree the N900 keyboard is not perfect. My main reasoning for not getting the mini however was the keyboard feel was more of less the same and I just hated my n97 one. Ideally a nice 4 row layout and yes a bit more space would be nice but nether device is perfect.

As for the ui speed the N97 when I first got it (first week of release) was practically unusable it has improved a hell of a lot but its nowhere near as quick as the N900 from opening a message hitting reply and starting to type.

I miss Google Maps and Spotify on my N900! The major annoyances of the N900 are

A) Lack of official MMS support from Nokia.
B) Lack of any DECENT GPS Programs
C) Lack of Google Progs (something which could possibly be resolved with MIDP2 but ive not had the time to play)

Anything else is non-essential.