Well, didn't we all just crush a new owner's dreams! Possibly a younger driver with a first car or maybe first nice car (after all, if you have a Civic and a M6 in your driveway like me, which one are you going to grab the keys for - unless gas is over $4? Ans: no-brainer: the Civic is a tin box with cloth glued to its interior)
OP: Mazda had a solid plan in 2005: a car for everyone. The 2.3 is economical like the Accord LX and Camry L of the day, and the V6 was a much better alternative to the Accord V6, Camry XSE and Altima SE because it has solid handling with no McPherson front struts and more power from its 3.0L.
But the 2.3 MZR isn't the stoutest engine. Its no Toyota 22R, Chevy 350 or Subaru EJ22. At this age, it just won't take much abuse, or even neglect. Seriously. If you DON'T have lots of experience and knowledge on engine maintenence, dive in with this engine. Keep up on the oil, MIL/CEL messages, gas and spark. If the car is not your DD, and you REALLY want to mod it, I would be patient and start looking for a wrecked CX-7 with the turbo you could get as a parts car and pull the whole drivetrain AND electronics "nervous system", spend some evenings detailing and building the engine out and wait for the current engine to throw a rod.
Then you could spend a whole winter in a freezing garage with a laptop, diagrams, service manuals. doing a high-quality build that will make everyone jealous and you can be proud to have done yourself.