My wife's current car is a Y2K Legacy (but I make the payments...go figure) with the 5MT. Having owned a '96 Legacy previously (2.2l 5MT), I can honestly say that the new Legacy's are a quantum leap ahead of the older body styles in terms of refinement. The car not only handles better (my opinion), it also has far better build quality. That having been said, the older 2.5GT's are probably a little faster since they're about 200lbs lighter. Because of the 3300+ lbs weight of the new Legacy's, your TS is probably faster than the new GT's. Also, that weight means it won't handle like your TS, but I'll bet at high speeds, the Legacy will feel far more stable with the longer wheelbase and the new multilink suspension. I've driven the carin the BC interior a few times (Nelson, Castlegar, Cranbrook, areas) and that car will do 160+kph and you feel like you could do it all day. My wife LOVES the Legacy and how it drives!!!!
Also keep in mind that this car is meant to appeal to a different segment of the market. I'm 34, married, and two kids under the age of 6 (probably the younger end of the Legacy spectrum). The Impreza is generally targeted toward younger buyers with no families, or younger families.
I also hate AT's, so we had a choice of the Brighton Wagon or the GT Sedan with the 5MT. Everything else in the Legacy lineup in Canada is sold with an AT. As far as suspensions set-ups are concerned, since the Y2K is a very new model, there is a VERY limited aftermarket availability with this car (believe me, I've been looking). If you go the route of the new Legacy, you will probably be driving it stock for awhile.
AFAIK, the 2.5 will stay as the base motor in the Legacy lineup with the H6 offered in the Outback with AT only (maybe GT limited). The 2003(?) GT's may come with the new 2.0l turbo that is supposed to be offered in the 2002 Impreza WRX NB.
My advice to you is to hold on to your TS for a year or two until the new engines are available in the Canadian market.
BTW, I'm thinking of getting an Impreza Sedan as my work car. Are you happy with the TS, or are you wishing you spent the extra dough for the RS?