Crumbs, that just reminded me of something. 'Back in the day' (1990s), I believe, to compete successfully at club level it required 5x sets of £30 cells. To compete at regional it required 5x £50 cells and a motor skimmer at least. Which were very expensive... Now I own two packs of cells which are fine and cost a mere £37 each new.
I might be totally wrong, but I honestly believe if you are up at the sharp end regional or national racing you will be sponsored so the cost of that second car (if its really needed) is probably not the end of the world (half price or free).
At my level (club racing at the back!) two cars will make absolutely no difference to where I finish at the meeting. But I
am going to buy a second car, but
only so if I badly shunt the first I don't have to go home

(rarely get to go racing with work and other life commitments so have to make the most when I can).
Besides, peoples are forgetting the down side of running two cars - you've got to clean and maintained two which is a lot of work

On a serious note also, swapping from a 'wet' car to a 'dry' car or vice versa has got to take mega skill to pull off as I bet they are very different beasts to drive so not so many people other than the top top drivers are likely to be able to pull off a competitive advanced perhaps? Which goes back to the fact they are likely sponsored with cheap free cars?
I guess what I am trying to say is a large budget always brings advantages, two cars or one, as I found in the 90s on the negative end (my car dumping, competitors not dumping towards end of race). Just a fact of life :-s