I have a 2000, Vintage Sunburst, Gold Hardware, ES 175 and if you only paid £1500 for it back in the day then you got a very good deal. I've had mine since 2003. If yours is anything like mine then they are very good instruments. They are very sensitive to bridge placement and string choice which can make intonation initially hard work to get right, but once dialled in, and respect given to the floating bridge, then they deliver fantastic tone. I've seen people have the bridge pegged or even stuck down - I can understand the reason if gigging hard but personally I wouldn't want one that had been modified in such a way.
If in good condition then this is worth at least what you paid for it. These turn of the century Nashville ES 175s are generally very good instruments indeed. £2K ??, at a push - but even then the buyer is getting a lot of guitar for the money. £4500 new - no, I'd probably go for a used L4 - CES instead - I'd love one but it would mean selling the ES-175, and I like it too much!
If you want something a bit more flexible then try and find a Howard Roberts Fusion III to demo. These give you the smooth tones of the ES 175 and will deliver a clean bite too. They are, generally speaking (as it depends what PUPs are in place) not as aggressive as the 335/345s. They are also a smaller body and so more comfortable. I much prefer HRFIII to the 339/359 series'. They aren't easy to find, but can definitely be had for the value of the 175 - and are much easier to gig with.