Any particular reason for the Forester? Do you care about performance or is a NA variant ok for you?
I've had our Legacy GTB (twin turbo) for almost a year now and it has been faultless. It's of a similar age to your car (2002) and other than the big 100km service it's required nothing other than petrol. Talking of which, the Forester XT (the turbo variant) is just as bad as the Legacy for economy : expect 25mpg on a good motorway run if you're very careful with the right foot and 20mpg around town.
The Forester interior is just as bland as the other cars which it shares the platform with. It's not offensive but it is uninspiring. I personally don't mind this but it can put people off.
The room inside a Forester is really good. It doesn't have quite the capacity of the Legacy but it's still very good.
I don't know how you'd find servicing. Here, there are plenty of indys who are used to Subarus as so many of them are on the roads. From memory, it's certainly not like that in the UK so you may be more reliant on dealers.
I test drove two Foresters before buying the Legacy and I enjoyed them. The XT is rapid but it didn't have quite the space we needed and I couldn't get over the 'on stilts' look they have. They're extremely capable cars (in turbo form, not sure of NA) and the engines are extremely reliable. The auto boxes from this era often get criticism and cost a lot to fix but, as I said, I've experienced zero problems with my Subaru.
I don't know if any of that helps as the Legacy and the Forester aren't (quite) the same car but I hope you get something from it.