As £400 will get you some reduced price specials (Cyrus, Arcam, Audiolab to name three) from significantly higher amounts, then you could make a significant step up. Arcam have been the most prolific with some truly jaw dropping cut price gear. The CD192 and the DV135 have to be up there in some of the best bargains going (DV135 £900 widely available for £299? Yowza!).
Equally, it's not necessarily night and day. My old Kenwood DP7090 (£400 in 1998) was hardly outshone by a similarly aged Linn Mimik (about twice the price of the Kenwood in its' day). Some players will be very different - Exposure and Audiolab will pin you down with a vibrant presentation, so it depends on your taste and wants from your gear. If you keep with the same kind of sound (let's say warmth as we're talking about your Arcam) and buy a higher priced player with similar tonal qualities, you might be looking at subtle differences - greater scale, slightly more presence, depth, a touch more detail, deeper bass and so on, but not at the expense of the overall character.
Lastly, if you are happy with the sound, then it might just be tweaking, in which case talk to some dealers and see what they say, which cables they recommend and if you can try some out. last but not least, have a think about the used market here - £80 will get you a higher priced interconnect, so your money goes further and it might be all you need to spend to get the change you want to achieve. Or, you might need to spend the full whack. It all depends.
Rega P3 & AT 440MLa / Marantz SA7001 KI-S CD / Marantz PM6010 KI-S amp / Mission 752 floorstanders / Audioquest Type IV / Audioquest Copperhead
