References to prices all need to state whether they are retail, private or trade. Main dealer gross margins are £10k which is why it is important.
Also we need to think how much a same age, same mileage GTS (of either gearbox) is worth over a 4.2 once they are 3/4+ years old - £5k?
As for where prices are going, once these cars are over 3/4 years old they depreciate at £5-7k pa trade to trade (or retail to retail).
Finally we also need to look at mileage as all the cheap early 4.2s come with c10k pa mileages (this is important as that is the mileage I am doing!!). FWIW CAP hits 1k of extra miles for about £300 on these cars, so a same age/spec 30k car is worth £3k more than a 40k car.
Cutting to the chase, seeing a 57 plate 4.2 for £29995 retail in autumn 2012 is unlikely IMHO unless it is a 60k+ miles car. Retail next autumn is likely to be £35k for a 40/45k mile five year old 4.2 IMHO.
As ever with a Maser, you want a bargain then go to the auctions. £30k will buy you a shabby 57 plate 4.2 at auction within a couple of months but that will be a 40k miles, silver unwarranted car, posssibly with a red, bordeaux or grey interior. Personally I think better value lies in a newer 4.7.