Any point upgrading my all-in-one system?

[MrSafety]

Folks (already posted this in the LCD projector forum - no replies)

Having searched the forums I suspect there is no clear cut answer to my question so am preparing myself for disappointment but here goes:

I have a bog-standard LG all-in-one system feeding my HS10 through s-video using the multi-cable which came with my PJ. I am happy with this setup but am thinking about upgrading my DVD source to a better all-in-one. I am constrained by a number of things:
(1) aesthetics - hence going the all-in-one route and also my speakers are wall-mounted and because of the room geography any replacements need to be small and wall-mounted as well (hence looking the likes of Sony's DAVSC5 - even then much-rated Denon's speakers are too big for my purposes)
(2) cabling practicalities - when I installed my PJ I had to go crawling through roofspaces and the like to thread my multi-cable from the DVD player to the PJ and I don't want to revisit this in a hurry: so constraint number 2 is that I want to continue to use this cable.

So, question in two parts:-
1. Is there any point going for a progressive scan DVD player? I'm not going to spend more than £400-ish and I assume that the scaler in my HS10 will be better than a DVD all-in-one system in this price bracket.
2. Will feeding my PJ component via the multi-cable give me any noticeable improvement in PQ over s-video through the same cable?

I don't want to waste my money on something which won't give me a reasonable improvement. Since I'm not desperate I can always wait another year ...