The plans I make are very on and off lately. This one is more for the layout, which hasn't made much progress lately and a lot of plans of mine get set aside for later while I work on others. They do change and evolve when I get more ideas as I go too, usually the general idea is the same but some of the smaller ideas around it change over time. I think the Hornby model will be a good base for a detailing project, and with that I could potentially get it look really good. The thing about the Bachmann model is that they mostly come in Power/Trailer 2 car sets, and they are way overpriced in my opinion. In Australia, you could get a 4-CEP Southern Electric cheaper than a Class 101! It's also that I try to avoid too much changes to RTR as well, although it may sound stupid, there is always a chance of completely wreaking the model. Although I think this should turn out just fine.
EDIT: Although I find with purchasing from eBay that a lot of the listings end within less than a day. I don't mind the cost of scratchbuilding with plasticard, as I still have lots of leftover sheets from previous projects, and the price of a pack of three or so sheets is pretty decently priced. Doesn't necessarily mean I'll buy a second hand model, nor does it mean I'll use plasticard. I think it will come down to what I have already going on and what I end up deciding then. And anyway, one sheet of plastic typically can cover one car, sometimes a little more...