Most important vinyl component to upgrade first ?

The most critical unit in analog reproduction is the Phono Stage. There is absolutely no way to degrade a signal more than here [Only exception: Using MM Cartridge, then it is not necessary to think about a high quality Phonostage].
Your 1-5 list is correct.

The cartrideg I find makes a really big difference. That said a crappy phono stage will ruin anything the cartridge is sending it.

IMO the comment by TPReaves pretty much says it all, although Viridian also makes an excellent point in emphasizing the importance of a synergistic match between cartridge and tonearm.

I would add that more than a few very experienced audiophiles here, whose opinions IMO command a good deal of respect, have expressed the belief that a relatively inexpensive but suitably matched cartridge mounted on a high quality turntable/tonearm combination will generally outperform an expensive cartridge mounted on a relatively inexpensive turntable/tonearm combination. I see no reason to doubt that, as a general guideline.

02-02-13: Syntax
Your 1-5 list is correct.

Surely you didn't mean to suggest that the choice of cable is more important than the choice of turntable, tonearm, and cartridge, at least in situations where the length of the cable is not unusually long. Or did you?

Regards,
-- Al

Al,
good point. I thought about it when I read the list. From my experience the majority of Arms (inside) is far away from its possibilities based on their cheap, average cable inside. For example, a cheap Rega Arm can show very good results when it will be rewired, you can simply get the most out of it with such a modification. When all is done to get the best out of any Arm, then it makes sense to go ahead (not everyone can afford everything but when you have something which can really deliver what is possible from its design, it can be absolutely fine). Various SME Arms are another example for internal wiring.
Some Arms have good wire inside (Graham for example), here it makes sense to link a top cable from its connector to the Phono input.
Or another example, when you work with Headshells, most are delivered with very cheap leads. When you replace those with top leads, silver or copper, you hear immediately the difference, for a small investment about 35-60$. The cartridge signal is so fragile, you can't improve it, but a lot can be done to degrade it.

Dear Noslepums: I don't know if you still own the Clearaudio Accurate, SP-10, SME V, Linto phonostage, Bryston amps and DYS speakers.

I know very well all those items but the Linto phono stage.

The SP-10 is IMHO a very respectable TT especialy in nude/naked version ( with out plinth. ) but needs a good TT mat. The Accurate is a good cartridge but not the best match with the V tonearm and not because resonance frequency in between but because other kind of interactions/distortions generated in between. Bryston amps are very good units.

According with Linto owners and Atkinson measurements the Linto is very good performer with the drawback that can't accept the MM/MI alternative that despite what Syntax posted ( IMHO in that topic he really talk with no facts that could serve as foundation on his remarks. IMHO any kind of cartridge deserve the best at phono stage to can shows at its best. ) is always a welcomed alternative.

So what I do it if I was you is to go for a different tonearm to achieve better Accurate performance and from there you could move a head on the other analog links to fulfil your overall music sound reproduction targets.

IMHO what defines where to start a system up grade is the system it self and for any one of us not be sure which your system set up has no real sense to give advise. There is no rules on up grade in any audio system.

If you share your system items you could have more precise answers that could help you in betetr ways.

Regards and enjoy the music,
R.