Complete replacement is hugely expensive whatever material you use, and there is not a lot of difference between the better fake finishes and the real stuff. You are looking at £6-7k materials and at least as much again in labour to remove the old stuff, make good and lay the new. So could be the thick end of £15k. So, keep patching as long as you can. Obviously you can reduce cost by doing some of it yourself, but it is a back breaking and time consuming job. One alternative that is becoming more popular as the cost is becoming such a large proportion of the value of boats, is to strip the old stuff off make good with epoxy and then apply a coating such as Kiwigrip, or even just deck paint. Mujch more servicable and may not affect the value so much.