If you like the trigger job, and the grip/stock, and the half-lug barrel, and the front sight, probably. You can pretty much duplicate all of that except the barrel 'after-market' on the standard GP100, but it'll cost more than the difference in original price.
^^ I would definitely get the GP100. There isn't that much if any difference in price either between an SP101 and the GP100. The GP100 will handle the 357 mag a whole lot better than the SP101 will. The SP101 will be easier to CC because it is lighter and smaller frame.
Like VT said upgrading the GP100 will cost in the neighborhood of the Match Champion. If you get a MC then get the model with the adjustable rear sights.
I bought into the Match Champion hype about a year ago. I kept it for about two weeks and I'm glad I unloaded it on someone else. The "Tuned" action was laughable to say the least. My 70's and 80's vintage security-sixes are much smoother and much better finished that the MC. I did sell it at a nice profit though!