Ouch, I'd have been mad too with all that repair work. As far as reliability is concerned, I thought the Si was a pretty decent car all around. The issues typically discussed were the 3rd gear grind and rough shifts from 1->2. Stiff motor mounts fixed that problem for me, though I agree it shouldn't be a requirement.
I did have some clutch fingers break at ~50K miles but the dealership replaced the entire clutch and first three gears under warranty for me.
As for the power... trying to remember it stock and I'd probably agree. The issue was that 6k rpm was hard to get in later gears, and that's where it started to take off. Moving VTEC down to 4k and you'd go through gears much quicker, that and letting the car breathe with some good bolt-ons.
But yeah, stock for stock, the FR-S is a purpose-built car and engineered to do what it does from the ground up. The Si is just a higher performance trim level. Not to discredit the K20 motor, it's a beautiful thing, but it is tied down quite a bit stock and the I think the Si's chassis isn't the greatest.