I also owned an XR3i in red. I had mine in about '89/'90, when I was about 24. I would belt it around the country lanes of south Oxfordshire, so not too far from where you were. Where we differ is in that I hated that car with a passion, but I cannot remember why exactly. I remember it used to shift (by 80s standards) and yet I didn't find it fun to drive. It might just have been a poor example, as it was a few years old by the time I bought it. I remember the exhaust came loose after having it a few months and would catch bumps, so at night time I could see sparks coming off it in the rear view mirror. Foolishly, I kept driving it like that for some time, until one evening on the way home from work at the Milton Trading Estate I hit a particularly nasty bump and it sounded like the exhaust had come up through the floor of the car. I pulled over to inspect the damage. Couldn't see any, but there was a strong smell of petrol and the exhaust was now on the ground. I had holed the fuel tank and was lucky it didn't go up in flames. I called my father and he came out. We fixed the exhaust so it wasn't dragging and he towed me home, after giving me a mouthful.
Of the first few cars I owned, two that stand out as being fun were the Marina 1800 TC Coupe and the Lancia Beta HPE. I'm not sure what I was thinking when I bought the Marina ... it had a jacked up rear end, stupidly wide tyres, the smallest steering wheel possible, a padlock on the driver's door and could be started with a screw driver in the ignition. It was ridiculous and probably the most dangerous car I've ever owned, in that when it got up above 70mph it felt like driving on sheet ice. It felt so out of control at speed that it was terrifying, and yet fun at the same time. I loved the Lancia because it was the first car I owned where I didn't have to take a run up from half a mile back to overtake something.
I think my definition of what is fun to drive has changed according to my age, driving ability, and level of good sense. When I was a younger man fun was all about being on the edge. I expect that might still be the case now to some extent, if I had a particularly fast car to be able to indulge with, but with a TR and a Land Rover Disco, I have to find the fun somewhere else. I find the TR fun because it takes a bit more thought to drive than a modern and it looks great. And although the speed isn't a match for most moderns, having rear wheel drive makes it more fun than a lot of what is on the roads.
For pure fun in a car, I think you have to be young, carefree and not give a toss about piling it into a tree