Interchangeable parts is actually the reason why I love my Tamiya cars!! Suspension blocks, arms, axles, even pulleys between my TA05 and 415 all use the same parts..
Even with the new 416 coming out, the revised 5x10 front and rear uprights will be backward-compatible to the Lightweight suspension of the 415/TA05R/Evo 4/5.
Some people are even opting to use the 416 and 501x's larger 18T middle pulleys and even 37T diff pulleys on their 415's with the use of parts from other models in the same family...
Of course, parts on something like a Mini won't have much to do with the TA05 or 415 parts bin, but as long as you keep with similar style cars you do have a lot of options..