How much to spend to beat $1200 10yr old speakers?

If you go Quad...go with the 12Ls...they have a much fuller presentation...and just to let u know...I would hesitate to call them bright... they are very revealing in nature...and sound nothing like rolled of SPendors or other "old-school" brit monitors...their 3-d imaging and bass is impressive...and in the QUad tradition...they are very transparent....

ALthough the Swifts have garnished much praise...I have not been impressed with their sound...to me they sound thin,hollow, and very lean....I much prefer the original KEstrals...

Phasecorrect, i agree, i heard the hot rod kestrels a couple years ago hooked up to some cheaper (goldentube) equipment and they were pretty stunning- so transparent, holographic imaging and good clean bass response- i wonder how the new Kestrel II will be, but thats a whole other price range- the imaging from the swift's was pretty holographic but they may be a bit lean as you said- at the time i thought maybe it was the amp- also, they sit kind of low for my ears, making images a little short- but hey, less than $1000 new- i'm intrigued by the quads but i think they'll be hard to find here in oregon

I very much doubt that speaker technology has improved to where a $600 new speaker would even come close to a $1200 10 yr old speaker. Perhaps a $1200 new speaker would improve ... which is not bad considering inflation.
I think you'd have to try, but I'd be very surprised if you sell the KEFs.
If you wish for more bass then I saw someone else suggested a separate powered sub ... it's worth considering ... I added one to my 10yr old spica angelus and it made an immense improvement. I think I'll still have the Spicas in another 10 yrs now I have the sub.

For those on the west coast...I believe Gene Rubin carries the new Quad line...also...the Maggie qr12s...the ones just below the 1.6s...are a great speaker...and roughly 1200 usd...if you have the room...a must audition....

All things being equal...a ten yr old $1200 speaker should at least equal a newer $600 one...but I wouldnt get too caught up in price ...there are simply not that many good speakers in either price range...and both the $600 Paradigm Studio 20 and the Quad 11L outperform a number of more pricey monitors(both old and new)....a higher pricetag can be just that...I value performance over price