Obviously having an empty garage has become increasingly stressful for me.

So in the end I canned the four seat idea, and just started looking at cars that excited me but also wouldn't put me back in debt. To be honest, there was only really one choice that I kept coming back to.
So here we go:

It's a 1998 S1, with 92k miles on it. It's had a new engine and has a few rough edges. The weird thing is that's part of the appeal, in the past I've had relatively low mileage mint cars, and have always had one eye on the resale and house deposits. This car is here to stay, I don't care how many miles I put on it, and how much of a Trigger's broom it ends up being.
There are lots of great things about the car too: it's had quite a lot of money spent on it recently, there's a £6k bill from a couple of years ago, and some other big bills. Although the engine has 30k odd miles on it, it has only had a couple of thousand in the car, it's had the desirable S2 suspension upgrade also with only a couple of thousand miles on it. It's only a couple of owner car, same owner for the last 11 years.
I bought it from Will Blackham who many people will know of, and has a great rep. He was an absolute pleasure to deal with, and someone who exudes passion for Lotus. He seemed so excited about the car, maybe just his sales patter, but said when he first looked at it it was a bit dusty, but when he cleaned it up he was amazed just how good it was for the miles. I got in there quick, showed my interest before he'd even collected it, and looked at it the day after he got it, but he said he could have sold it several times over in the 5 days it was in his possession.
Picked it up yesterday, and I'm totally smitten with it already.
TL;DR: I bought a shonky leggy old Lotus.