Interesting choice of roundels for the top of the wings... Dates it as being in-service between January '45 to early 1947... Is that the only choice of markings for that kit, or did it have the Type B Roundels (the Blue & Red ones) as well?
Overall, I think the weathering is pretty much there for a post-war Mk IX (given the markings used)... It'd be pretty well-maintained once the shooting stopped... Yours is marked as a No. 43 Squadron, "The Fighting C ocks" bird... No. 43 Sqn flew Spitfire IXs from August of 43 to it's disbandonment in May, 1947...
When it first received the Mk IXs, it was based in Pachino, Sicily and remained in the MTO and Italy until moving to Ramatuelle, France in August of 1944, and ending the war in Italy, then moving to Klagenfurt, Austria. Sicily's climate would've been pretty hard on the paint of any aircraft based there... Also, the Merlin used a "Partial Loss" oil system, so some oil leakage would be pretty common, although not to the extent that the early Merlins on the Mk Is & Mk IIs, which would sometimes be black with oil from the rear of the engine cowl to the empennage...
Given all that, you can really do about any amount of weathering you want, including leaving it "as is".. I can't see the S/N of the aircraft, so I don't know if it survived the war, though if the Type C.1 roundels on the upper wing-surface are correct, it would appear that it did...