Some good suggestions, though I think cars like the Ferrari 456 and M3CSL are now outside the specified budget.
If you have the space I would buy two or three cars for the money as it both spreads the risk and probably has the potential for bigger returns. Rolls-Royce Silver Spirit and Spur remain undervalued at the moment for a good low mileage car. At the time they were making 10 Bentley to 1 Rolls-Royce so much rarer than the Bentley version. Avoid pre 1987 car cars and ideally go for a post 1990 Spirit II or Spur II with injection, ABS etc.,.. Low miles, condition and a decent service history are the key. Rolls-Royce has a positive brand image now with the new Phantom, Ghost etc and the Spirit/Spur has IMO got more elegant with age.
Jaguar XJ-S is another good bet, people are starting to realise it was never intended as an E-Type replacement but aimed at a different market. A new XJ-S in 1975 cost twice the amount to buy as the last S3 E-Types it was intended as a more upmarket gentleman express. I know I will regret selling my XJRS convertible (the only RHD car in existence) but a good early pre HE car should be a strong bet. They are rare as so many of the early 70's ones have rotted away but the good ones that remain are already appreciating. The best bet is an early V12 manual (they only made 351 of them) if you can find one that is rot free and reasonably original, though I think in the not too distant future a rotten V12 manual might justify the cost of restoration.
Another good bet is the Rover SD1 especially the Vitesse. Car of the year when it was launched and a very successful motorsport history. Ultimate would be on of the rare twin plenum Vitesse's built to homologate an updated version of the touring car. Again a combination of low production numbers and a tendency to rot means good ones are few and far between but IMO worth seeking out. Since the introduction of the Goodwood Members Meeting where they have a touring car race for cars of this period people have started to build £100k race SD1's to compete there, a good sign that the road cars will become more sought after.
If you do want to put £35k in one car I would go for a MK1 Sunbeam Tiger. Tigers have been on the up for a while now but I think are set for a significant rise. In the USA prices of MK2 Tigers have rocketed, I know of three cars that were sold at auction last year (2015) and they sold for $230,000, $260,000 and $280,000 respectively. None of the ultra rare UK RHD MK2 Tigers have come on the open market recently but if/when one does if the price reflect the US examples then MK1 Tiger values will almost certainly wake up as well. Bear in mind that there are approx 10 to 12 RHD MK2 Tigers -v- 200+ LHD MK2's and £200,000+ is probably not too unrealistic. Therefore I feel the days of the £35,000 MK1 Tiger are numbered and a pretty good bet for the future.
All this is IMHO of course but with the first three I have already put my money where my mouth is so to speak and I am fortunate to have owned a MK2 Tiger since the early 1990's.