The Speed3 is by far the best performance deal on the market these days. I've gone through this numerous times with my friends and my brother. We test drove a lot of cars.
It's much more reliable than the MSP from my experience because it was designed to be turbocharged. Granted some concessions were made to keep it that way, lowering boost in lower gears, and not making nearly the power the engine is capable of from just a tune. But if you keep it relatively stock, it should last a very long time. The oldest I know of in my circle of friends is an '08 with about 70k on it and the only real issue is his A/C clutch failed. He's not the kind of guy to take care of a car either, so I think a more loved car would do even better.
My brother bought an '11 last summer and loves it. I've driven it quite a bit and I even came very close to buying one myself on multiple occasions. I drove one back to back with an EvoX and I thought the MS3 was infinitely more fun to drive, while being much more comfortable as well. The only downside is that it feels tall compared to the MSP, because it is. Parked next to my MSP it looks twice the size, but there is nothing on the market currently that is as small.
The only thing I think will offer the same level of fun as the MSP is the BRZ/FRS, which you won't be able to get your hands on for a while, and will be frustratingly slow with only two NA liters. Turbo kits will be out soon, but then you lose your warranty and defeat the point of a new car. You also lose the very functional rear doors and full sized seats.
This is why my MSP is staying with me.