I think racing modification should start off with a selection of styles
RACING MODIFICATION: Choice of semi-custom paintscheme, sponsership logos, and Racing number on doors maybe roof and bumper. Peformance wise, it would unlock the highest stage of parts, but they won't be too flashy, Just stariaght out performance, like stage 5 weight reduction, purchasing a legit racing engine and parts, ultra light weight body kit and panels, designed for max airflow and adjustability, in other words this would be the most costly but would turn your car into a full out race car.
TUNER MODIFICATION: FUlly-Customizable paint scheme's, different levels of sponsership tags or none if not wanted, unlocks a massive amount of tuner parts, such as bodykits, engine decorations, tuned exhuasts, custom suspensions, and basically all the flashy stuff you would expect from the tuner world. Basically your paying a moderate amount of credits to unlock a higher level of customization and to be abler to trick out your car.
RALLY MODIFICATION: Basically the same thing as racing modification but dedicated to off-road use, meaning the same paint scheme numbers and features but with fog lights heavy duty suspensions, snorculs, etc.
THE SHORT STORY: If your serious enough and funded enough along with having already purcahsed all stage three parts, you can Upgrade to one of the Three Modification styles. Once access you would go to a part of the map and lcick on "RM Store" and it would have three choices
RACING CATALOG
TUNER CATALOG
RALLY CATALOG
Each with its own destinct online style catalog allowing for a detailed level of customization, example, a Racing Mod car could be Circuit or Drag, but everything in the catalog is full-out performance and very very expensive.
A tuner Could be a drifter, drag racer , circuit racer, obviously not on the smae level as a racing car, as in folowing regulations and what not, After market is whats its all about here and a bit more afforadable.
Then theres the Rally Catalog which would only focus on off-road use, expensive, and rugged is the name of the game with these parts
Purcahsing a Modification unlock registers you into RM only races, allows for purchasing of specialty parts, and allows for unique interior and exterior changes.
sidenote: on RM only races, Racing Mod'd cars can only compete with Racing mod'd cars, same for tuners and Rally cars, so you wont have a bunch of better than stockers playing with 600hp monsters, or a Tuner car upa gainst a racing car, unless its a special mixed RM challenge, "Drift spec Skyline vs. JGTC Supra" (Top Gear stuff lol)
By making this a diverse yet segmented setup, it allows for indepth tuning and for a multi-acspect game, where as you can have full out Drifters playing the same game as die-hard road racing fans,etc.
seems like an extremly good idea but you got to take in to account the seriousiness of making hundreds of defferent mods for each of the 700+ cars, takes alot of programing and alot of disk space, but then agian maybe they could set up something where you can plug your memory card into a port, that plugs to your computer and mod your car indepht online at a GT store, that too would probably require a fully dedicated memory card.
anywho thats my ideal setup for the next generation GT