Well I'd love priod cars as mush as tuners...
If I had to build a mk2 escort or a porsche I'm going for period style but if I'm gonna built a MkI Golf I'll have the alternative of a Euro tuner or a upgrade with modern parts...
Also other than car specifics aspects is something that you propably know since you open this subject...Period tunning is mostly about suspension,tires and motor and there is no source to get period tires or you get 3 diff sets of wide 13'' and 25 different sets of 17-18-19" which means less variety add to that that most models might come enginless or the builders don't real care about the engine so you get the point...
(from the above I put aside the muscle cars since there is huge variety and you can easily get model period tunning parts...
An excellent example of great older models tunned with modern parts is Laurent(GTI1800) which build in an awesome style and sort of make his own trend,I love his models and to be honest I like them ten times better than a period looking car...Simply it's the quality and the imagination of the build...I can see a pic of his model and I know it's his...it's Laurent style