Please evaluate my system...

Tim; You have a fine system. It is always easy to recommend changes to every component of every system. After all there is something better just around the corner. The real question is how to make changes and then be sure that what you hear is indeed an improvement. This is only possible if you change one item at a time so A/B comparison is possible. Whilst the DL103 is a fine cartridge and its performing way over its price/performance expectation I believe you may get get a lot more out of your records by switching to something like Lyra Delos. Your VPI is perfectly capable of handling the Delos and so is the Linn Phono stage. Good luck in your quest. 

A few OPINIONS on three of the suggested changes....  These are opinions based on my experience.  Others have probably had different experiences.  YMMV.

A nice and effective room treatment is just the addition of a lot of artificial plants.  Doesn't have to look like a tropical rainforest, just break up the reflected sound.  Will make a big difference and help reinforce the WAF.  

Vibration / isolation can be easy and inexpensive.  Vibrapod cones are very effective.  Maple butcher block works and looks nice.  A combination of Vibrapod cones and maple butcher block boards can make a difference.  

In my opinion, power conditioning won't make as much difference as an improved phono stage (1), room treatment (2) and vibration control (3).

What a horrible system! I’d be embarrassed. Come on man. Your stuff is better than at least 3/4 of the people on this forum. If it sounds good to you it’s good. Enjoy it. 

Tim, which power cables are you using & what is your wall socket?

Thanks for the advice. Few bits more info in case it's of value. 

Speaker cable is Chord Odyssey. I have some pure silver interconnects. 

I get the cart recommendation, I'm interested in looking at a high range for that. What sort of price / which cart, would be sensible to upgrade to? Thanks for the advice on the Lyra, will look into this.

With regards to isolation I have some in place, decent enough rack and some Sorbethene feet on most of the kit. I'm not convinced with the value of expensive isolation pieces I've tried quite a few and can't tell much difference. I'm on a concrete floor with the speakers so may have something to do with it. 

Never heard the difference between mains cables, I'm still not a believer having heard £3000 worth of them and couldn't tell the difference. I've had Ben Duncan mains conditioners which seemed to work well. 

 Interesting on the phono stage, I see the Linn is very well reviewed across the board, surprised it's coming up as a weak component. Not sure how easy Herron is to get in the UK, I wouldn't buy new there are simply too many bargains second hand floating around. I find the balance of the system to be fine so wouldn't want any more valves (not that the Herron has them), which could bloat the sound. 

Ultimately I like a big soundstage and although good I think it could be improved. 

Thanks, Tim