I'd also say this - and yes, I've said it before - in this case, it would be nice, and probably eventually cost-effective, to completely electrify the North Downs Line and build a South<->West spur at Redhill, complete with platforms, for Intercity/XC (Brighton-Gatwick-Redhill-Reading-etc.) trains, and also any remaining FGW services. The site known as "the old Ford garage" in Redhill (despite the fact that it's still very much a functional garage!) is safeguarded for this very development, but it's never happened.
(If no extra platforms could be added on a spur at Redhill, there is land available at Reffells Bridge, under the A25 between Redhill and Reigate, which is blatantly earmarked for rail development (having read up on local records, spoken to my friends and family who, like me, live near the site, and examined local maps very closely). This is very much a digression, and I apologise!)
The key to running a successful frequent service on the Brighton Main Line and the North Downs Line would be to advertise it as a bypass of London (which, as has been pointed out, is not a city that's ideal for travellers moving between stations, even if some people, like myself, can make connections very quickly) and then make sure connections can be made to Coastway services, any services deemed crucial at Reading, and perhaps services from Kent at Redhill and Brighton. In addition, Redhill is a town that was built around the railways, but people are giving up because of fewer and fewer trains stopping there, so reintroductions of services would be able to be used as a massive marketing boost and would be great for the local economy.
If more paths are needed on the BML, why not reopen the Uckfield-Lewes? Clearly, if there is demand for more paths, and no more are available, more infrastructural capacity should really be added, because demand normally increases! Any services to and from Brighton that do not call at Gatwick Airport and Haywards Heath could be sent along this route.
Any further paths needed between Redhill and Reading would need to be added with the Wokingham resignalling (let's face it, even if my suggestions were put into action, it wouldn't be before that's done) and the further platform(s) at Reigate, one of which is planned. A consolidation of Dorking Deepdene and Dorking Main, with additional platforms on the North Downs Line, would be a good thing, in my opinion, and would reduce confusion. The old chord that I believe was in place could be reinstated, but North<->East instead. Since there are so few services calling at Betchworth, Dorking West, etc., these shouldn't be stations where problems occur.
Perhaps we could also see a link from Guildford<->Heathrow, with the NDL FGW services being significantly modified to become Gatwick-Heathrow services. Perhaps even the Portsmouth Main Line could link to Heathrow... I fantasise!