I agree, I only want one of each, I'm not greedy!
Here's the deal, pre getting back into Ibanez work-horses (which I cannot speak highly enough of - amazing guitars!), I used to be a Tele guy almost exclusively, I think they're awesome guitars. The one I own now is the 'finest' one I ever owned, in that it is a truly beautiful example. Every time I post pictures of it on the internet Tele folks swoon, it's just a very nice one. That is part of the appeal, it is a sumptuous instrument. But then so is the Les Paul.
Thing is, as many of you know, you don't have to shell out a lot to get a great working instrument, and I'm almost too scared to play the Tele because I don't want to ding it or mash it up. It would make me cry.
I don't really have the resources to justify lots of expensive guitars so I've ended up with two more pricey ones and a couple of nice beater players. I hope it goes without saying that all my guitars play well, if they don't they're out the door, whatever the price, same goes for sound, I haven't owned a truly bad guitar in years.
I have a mint 75 hard tail Strat, and the space for the other £1000 plus guitar is taken up by the Tele. The Strat will never be sold as it has sentimental value, it belonged to a notable musician, and was given to me on my 21st birthday because it is the same age as me.
I don't think Teles should be kept in glass cases, they're workman-like guitars, and to me at least are all about function. Sadly mine is too pristine and I don't feel like playing it in case of the inevitable first collision with the wall or a cymbal. I've had others, with knocks here and there, that I had more playing enjoyment from if I'm honest. Some of those were quite cheap, possibly the best player I ever had was an MIJ 50's reissue with the most amazing V neck. I tinkered like mad with that guitar and it was superb.
Les Pauls on the other hand are beautifully made things, and I can see me justifying the cost with the luxury if you see what I mean. Fenders are two planks screwed together, Les Pauls have flame tops and set necks, and are gorgeous pieces, more craftsman than utilitarian - almost the opposite to a Tele in fact.
I'm thinking I may well do this trade and then get something like a used Road Worn Tele, because I can't imagine not having a Tele in my arsenal. Having been a Tele player for so long I almost think of them like an instrument in themselves, there's stuff you do on Teles that you just don't do on other guitars. And then we come full circle, and I think - well I've got a GREAT one already! Why would I want to get rid of it? And besides, if I don't ding it, the next person will, so am I being daft?! So possibly you see part of my my quandary.
Further, I've owned just about every sort of guitar going, but bizarrely never a Lester. I've had an SG, an Ibanez Artist (70's), a PRS Custom 24, etc. but never the real thing. And I've long fancied one, and here's someone offering me one on a plate.
The lack of Tele won't really hurt my sound too much even if there's a gap between replacing it as I have the fixed bridge strat which does there or thereabouts. But then do I really need another two humbucker guitar now I have an RG 570 again? But then I've enjoyed the twin humbucker sound and the flatter radius feel so much again, would I prefer the LP to my Tele.
The other thing in all of this is that I think the guy with the LP is selling himself short. I think his guitar is worth a bit more than mine, but I've alluded to this and he seems happy still to go ahead, so financially I would be up if I swapped. If I hated it in 6 months I could flip and probably be better off anyway.
Other than that, they're both lovely instruments, there's very little to choose other than one's a Les Paul and one's a Telecaster. Both come pretty much as good as new.
Thanks for listening to my life story.

It was cathartic! I posted my question on this site over many other forums because given the guitars in question I guessed you guys would be least biased, and also because I've always rated the opinions on here. You all helped my buy a peachy Ibanez RG570 (and avoid some less than peachy ones) so I trust the knowledge you kindly impart on here.
If anyone can be bothered to read all that, I hope it helps explain my decision making angst at the moment!
Above all, thanks for the great advice so far, and keep it coming, this site is great!