GFV Are designed to leave equity in the cars thats the point of them, the trick with a pcp is to put in a small deposit so you don't have deposit erosion. If you put in £3000 to get a lower monthly payment the GFV is calcualted on the car bought, the mileage your doing. Lets say the equity is fixed at £750, You would have lost £2250 and the reduced payments wouldn't account for £2250 worth of interest and if you don't end up buying the car its really lost money.
Chip in respect to mileage on cars your wrong. The condition of a car is worth more than mileage agianst a book value. I'd never lose sleep over a car over miles any more than I'd satnd a car up thats low on miles as that just simply never happens. The only time you would ever be penalised on a pcp is if you were hadning the car back to the finance company or VT'ing the car. In these cases the finance company will charge for excess mileage and damage as its their vested interest to get their money back before they send the car to a closed auction. If a car came in px on a pcp and had a ridiculous amount of miles over what was agreed (say 60,000 on a 30k agreement) then clearly the customer would lose out. However if the car came back in 15k over there is enough magin in cars and enough good deals on for it not to affect the deal (certainly wouldn't be as good a deal if the car came in on or below miles). The condiiton however is far more important, it costs £150 to paint a door etc so a damaged door, broken bumper and knackered wheels have far more impact thana car over book miles ven on a pcp agreement. I have seen cars come in looking like they have finished the Dakar rally and people oblivious to the fact that they need to look after the cars for 2/3/4 years and not just abuse them.
In respect to cars that hold their value better there will clearly be a premium involved in buying them in the first place so quite possibly putting the OP off. Mini for one might have good residules but they like Honda and Volvo also have their own market where by their cars are worth far more back to them than anyone else so creating a bubble that in can be very hard to get out of. I for one have no end of issues with Volvo customers and the fact the trade doesn't see the values in the cars anything like the dealers do. This means when you call for an underwrite you are low balled by a dealer and traders and yet Volvo will give their own customers ridiculous value on their cars (I digress from the main point slightly but ou get my drift).
In the last ten years alone the market has changed massively with respect to PCP's. I remember working for Renault when they forst introduced pcp's and offering people 6% apr on a pcp vs 18/25% apr on a 5 year HP agreement. PCP is a massive part of Renault now and they offer rates from as little as 2% apr. So irrelevant as to how the car will depreciate its still going to work out a very strong deal. The manufacturer I work for no longer supports pcp's but has the strongest new car offer in the market place at present and makes the point of a pcp null and void against the offer.
For the OP look about, consider new cars, look at the benefits that dealers are offering as there are alot at present and certain brands (Renault being one) are in alot of trouble in respect to new car sales. Use this as a stick to aid you in getting the best deal possible. If it still seems expensive then you still have the option of a straigh forward hp agreement on a used vehicle. No need then to use the dealers finance as there are deals in the market place for over £5k of 7% apr. At present it is a buyers market so take advantage of that. Any question with reference to buying drop me a pm I have a little bit of insider knowledge