E39 to E63 - mad?

[Collectingbrass]

I've been using an E39 525 as my main car for a couple of years and I'm contemplating a change to an E63/E64 630. The E39 gets me somewhere around 28/29mpg most days, has 110,000 miles and I would probably be lucky to get £1500 for it. Autotrader, that evil temptress, suggests I might get a 2008 630 with 83,000 miles for less than £10k. Leaving aside the actual car (here by the way http://www.autotrader.co.uk/classified/advert/2016... as I am not yet in a position to buy, is this madness? The only reason for contemplating the change is I'm a bit bored of the 525 if I'm honest and I was browsing while the sustainability wonk was droning on in yesterday's company wide meeting.

[Collectingbrass]

Just by way of an update, I decided I would make the change when the remote element of both keys stopped working on the E39. I took on board the comments above, shopped around and found a manual 630 with my initials on the bog standard number plate. Which should have been my first warning as this car was in West London and you only get my initials on a reg plate in Scotland. I googled the dealer as it really was too good to be true and this was a good thing as their feedback was atrocious. (BTW, I wont name & shame here but if anyone wants the details PM me)

So back to Autotrader, select coupes only and keep looking. Oh, what's this, a BMW specialist with one with a good history, all the options I wanted and a 12 month ticket to boot. Well it would be rude not to go and have a look. Oh no what a shame it's a 645 with a V8. Oh dear that engine note is terribly seductive isn't it. Ooops, I appear to have bought it, oh dear, how sad, never mind. What's that officer? Only in Germany officer...