With those IEMs you should get a pretty good idea of what you're looking at with just the stock tips.
I can't provide any feedback on most of the sets you're considering. The only ones I have heard are the 1964-V3, Westone UM3X, and the Cardas. I thought the Cardas was lacking in clarity for the price and can't recommend it at all. It's still sitting in my desk. The 1964-V3 has borderline basshead bass and doesn't seem like it would be a good fit for you, especially coming from an SE210. In that price range the Alclair Reference would be the custom I'd recommend but I still don't think it's a great fit for you. The SE535 would work better for you than all of those, although I haven't heard the SE535 SE.
From your requirements I would also suggest the StageDiver SD-2, which is not unlike the SE535 except that I didn't have as many nitpicks with its treble. It doesn't really have enhanced bass, but no less than the SE535. The mids are not forward, but not recessed either. Treble isn't bright and doesn't have too much sparkle, but again it's better than the SE535 I heard in that respect. Other than these reservations it ticks all of your boxes.
Sorry for taking a while to get back to you, been away without a laptop for the last few days. Thanks for the response & recommendations! Really appreciate it mate.
I've had a look into the SD-2 & it does seem rather intriguing based on your review as well as others - certainly a strong contender next to the SE535 SE. It is the priciest option though, so I'm determined to find out how it measures up against the SE535 SE & some of the others before I make a final decision. How would you say it compares to the W4/W4R, as that was an option that I was initially considering? Following some more extensive research, I decided that the bass might not be quite fast & responsive enough for what I'm looking for straight out of the box, along with a lot of comments about it being somewhat 'flat' in a sense & was led to believe I would need an amp to really appreciate it's unique signature.
Also, how would you rate those the SD-2 & W4 against higher end custom models such as the 1964EARS V6 & Unique Melody Miracle purely in terms of sound quality since you've tried them as well?