I think you definitely need better speakers. The difference you will get between a Rotel RCD-1072 and that Naim CD5i for 1k difference in price is much much smaller than the difference you would have gotten by getting a B&W 703 or 804 speaker, though the 804 is way out of your budget, it would make the best upgrade path for you to sell ther other stuff in the future and hear nice benefits as you upgrade.
I tested most of this gear before I moved on to more expensive stuff myself and the Rotel CD player with much better speakers would have been a huge sound difference over that Naim player with B&W 600 speakers...
The simple way to figure it out is to test more thoroughly. The Rotel RCD-1072 with a B&W 703 would have been the best choice IMO. The Arcam integrated unit should be fine if it allows you to use a bypass mode for the CD player. You would have to come up in spending though.
B&W 703 pair = $3000 (804S is $4000 per pair)
Rotel RCD = $600
Arcam DIV A80 = $1300
Total = $4900 (if you must, save more money)
There is no definite percentage. Like Shadorne said though, you get more from your system by spending more money on speakers than most other components. This doesn't mean buy crap for the rest of your equipment though. That Rotel at the price is one of the best source deals out there IMO, unless you are willing to spend 6k like I did on the Ayre C-5xe.
Also for $1600 dollars you could get the Arcam Solo instead of a separate CD and an integrated amp. The Arcam Solo is an integrated receiver and CD player all in one. This makes sense to me if that is what it takes for you to get a better speaker like the B&W 703.
Starting at this price level, if you are thiking of upgrading slowly, I wouldn't bother. I would buy something you can listen to and enjoy for a few years, then buy some really nice gear with the plan of upgrading slowly further down the road. That's just me though, most people probably won't agree. It is just a very low price point to start at, and you will do better with good companies gear that is highly integrated over separates.
If you go with the solo you can probably do the best, all USD:
$1600 = Arcam Solo (integrated amp/receiver/cd player)
$3000 = B&W 703 pair
$4600 = Total
Or you could have a total of $5600 if you get the 804S speakers instead with the Arcam Solo, which would leave you a very nice upgrade path to work on with the rest of your gear.
The Arcam Solo has been getting kudos for all it offers in an integrated package at a great price. The B&W speakers always get awards at all levels... but the higher up you go, usually the better the speaker is.
Well that is my advice for what it is worth.