It sounds like you've got more of a regime going than you may think. Some people hate interval training but I always loved it, short intense bursts, rest, then go again. Change the intensity to suit your needs, fitness level etc. Good for in between the longer steady miles and very beneficial in terms of endurance and strength. Great prep for an event.
Turbo trainers are extremely worthwhile imo. Very convenient when you haven't got much time, it's too dark and/or the weather's really crap. Helps if you have a bike you can leave on it, then no faffing around taking rear wheel and spindle off (not that that's a great hardship), but less excuse not to use it. In winter set up your good summer bike on it, using winter bike for outdoor runs, and vice versa in spring/summer, switch over and stick your winter bike on it. We have mid range Tacx turbo, does the job. There's some decent turbo training dvd's around, hill climb ones etc. Helps you stay motivated and sometimes better than staring a the garage wall. Preferable to watching a film, never been one for watching TV whilst exercising.
I'm out on the mountain bike tommorow, with the family, down to a local country park with an active trail. They also have a 2 mile outdoor track and might take the F2 round the track a few times, if I can be bothered, though that's better saved for a solo visit, with no distractions.