Best bang-for-the-buck is clearly the larger rear sway bar. I'm not sure a WRX bar would bolt up - my guess would be no. I
think I may have tried to do the opposite - put my old 18mm bar on my sister's WRX wagon, and it didn't fit. Anyway, with my first 2.5GT my first mod was that 18mm rear bar and I was honestly amazed at what a difference it made. Even in day-to-day driving, taking my favorite on/off-ramps at moderate speeds, it was definitely noticeable. With my current 2.5GT I have a Whiteline 18-20-22mm that I think is set on the middle hole (I'm on deployment right now, port call in Guam, so I'm a few thousand miles from my car

). I had it set at the max setting for a while and snapped one of my stock endlinks at an auto-x - oops! Now I have MRT endlinks, which didn't make any noticeable difference, but at least they haven't snapped in half. With stock springs and struts and the larger rear bar I generally take FSD (Fastest Subie of the Day) because I pretty much rule.
There are some who don't like the ALK, even with the softer "street" bushings, because those softer bushings are still firmer than stock and cause a bit more harshness (or so I've read here in the Suspension Forum). I plan to get some MRT caster/camber plates to allow me to get even more caster than the ALK provides without any effect on ride/comfort.
I'm also planning on doing Koni strut inserts (waiting at home for me already) and Ground Control coil-over conversion sleeves. Koni does make inserts specifically for the Legacy struts, but the part numbers aren't obvious from looking on their website. I have the P/Ns on my laptop, which is up in my hotel room. If anyone is interested I can post them later.
I'll probably go with spring rates in the 300f/250r range or something like that. The Konis and GCs will give me all the adjustability of "real" coil-overs for a helluva lot less. I spent nearly $2k on DMS 40s, was I think the 2nd Legacy owner to have them in the US, and after a year I returned them because I was sick of the lack of durability. I don't anticipate any such problems with the Konis.
Pat Olsen
'97 Legacy 2.5GT sedan