I think with a little cash injection then it would be possible to have a rotation of at least 3 or 4 tracks. Silverstone, Brands, Donny, even Rockingham. As much as I'd love to see them also at goodwood, thruxton and castle combe. Those are circuits better left as the classics that they are.
Don't get me wrong - having had my motorsport education at Brands as a wee sprog, it's 15 years behind in F1 terms, and to invest in it to bring it up to F1 standard, much as the plan was exciting in the late 90s, would ruin the atmosphere of the place.
Rockingham suffered from poor marketing IMO, and I believe also from the CART/IRL split, which lost some of the European audience. Also I suspect if they'd cut the prices, they'd have had a successful race.
Silverstone, is a classic track, within the limitations of its airfield origins, but they always tinker with it, although the new plans look to be an improvement. I've never been a fan of the Abbey chicane.