You say that all the work you have done has made you stronger, so perhaps you have converted body fat to muscle mass, and as a result you have not lost any weight.

When you were on the trainer over winter did you grind or spin???

In regards to the weights versus water aerobics it really depends on what you are hoping to achieve. As han-grrl mentioned weights would most likely build more muscle mass, and this will help you on the bike, but there are other means of gaining strength without doing weights.

I do attend water aerobics once a week, but it is more of a relaxation thing for me and it gives me a chance to work muscles in the upper body that I never use without bulking them up.

If you really want to do something off the bike pick a long aerobic activity. Swimming is a good form of cross training as it is low impact and high repetition.