As far as i know all first generation hatchback grills (07-12) are fully interchangeable. I personally don't like the look of any chrome on any modern import cars. But to each their own. What kind of grill do you have now? If it is the all black grille i would buy it from you, if you chose to upgrade to a different grill.
The cost effective engine mechanical mods are a catback exhaust system and a header if you want (3 different companys offer a performance exhaust manifold (header)), cold air intake if you choose, but they don't help all that much for the cost. You are better off making your own in fact for the price of new ones.
Uprev is an engine management company offering tuneability on new platforms. As far as i know they have the MR engine PCM "unlocked", and you can buy various packages with the expensive ones offering more functionality and the base ones offering no end user tweaking. UpRev - Engine Management Store
You can buy a package, then go to any Uprev certified dyno in your area and get the car optimized.
If you are serious, Versaspeed.com has a lightweight flywheel, heavy duty clutch kit, lower final drive, helical LSD, and all the usual exhaust and intake stuff (and more). I got the lightweight flywheel from there and it was well made.
Also, the MR20DE engine from the Nissan Sentra (Sunny in that market?) 07-12 is a bolt in swap, no modifications needed or PCM or harnesses, 20HP and 20 TQ more than stock 1.8, probably more with mods.