For me personally it'd be a waste of money. I'd much rather walk for as long as I can as often as I can. If you have the time (which I don't either, working 9-5 and with two young girls & a hubby that works evenings!) and think you'll stick at it, then go for it. It wouldn't be for me though. And I've been a member of a gym. Why not arrange to have a 'trial' session and see what you think? Or try a variety of classes (pilates/yoga, boxercise, aerobics etc. etc.) and see if any of them appeal to you? Again, I'm just suggesting this as for me- a years subscription to a gym would be money wasted?
I love the gym, it's like my second home! It's my place of sanctuary where I can sort my thoughts out and no one can disturb me. Have a chat with one of the trainers there, explain what you would like to achieve and ask them to draw up an exercise plan for you. This is much better than just going it alone not knowing if what you're doing is right. Good luck and I hope you come to love it as much as I do lol!
I personally haven't been able to go to the gym since starting LT as I don't feel up to that level of intense exercise. So, maybe you should see if you can have a trial as you might not be as up to it as you think.
Also, I've heard people expressing concern here about too much exercise triggering starvation mode, so perhaps explain to the gym staff what you're doing & steer clear of a lot of cardio.