When to stop investing money into the GT??

I have responsibilities too. I am trying to get my business off the ground and I also have a 1 1/2 year old to worry about. The only thing that I do to my 2 Mustangs is the regular schedules maintenance. I haven't done any mods on any of them. I don't want to spend any money on mods just yet because both of my Mustangs are still on the 7 year/100,000 mile ESP Extended Warranty. When the warranty runs out, I would like to put a really loud Magnapack Catback Exhaust on my 2001 GT. I may also get the K&N Air Filter system.

As for my 2002 V6 Mustang, I am going to keep it completely stock with the exception of maybe getting some 17" GT Bullitt style rims and tires in the future. I really love the way the GT Bullitt rims look on the 99-04 wedge shape style Mustangs. There's no sense in spending money on modding a V6 Mustang when I already have a GT.
I would rather save my money than spending it on heavily modding my Mustangs. A car becomes a money pit after 4 to 5 years of ownership once the mileage hits above 40,000+ miles. Money has to be spent on things like tires, rotors, brakes, spark plugs and wires, and other major things which start needing replacement that can cost $500+ each time a major repair is needed on these cars.

If I were you, I wouldn't spend anymore money on modding your Mustang. You could put down a deposit in the future for a brand new Mustang just from all the money that you would be saving from not modding your current Mustang. You will never get the money back that you spend on modding you Mustang. Save your money and just spend it on the regular scheduled maintenance.