I just wanted to jump into this conversation. I started riding this time last year but did very little (IRL) until about mid May. Probably about 600 miles from May to Sept 1 including a metric century.
In Sept I started riding in my very hilly neighborhood, saw some improvement but still not too good. I started Zwift exactly 1 month ago today. I should hit level 10 in two days, this Friday. I have set myself up for a personal challenge, that is to hit level 12 and complete the Everest Challenge by the end of the year. If I do that I will attempt the Alpe on New Years Day.
Last night I rode to the radio tower for the second time. Tonight I'm going to do it again, then a group ride on Friday and to the tower once each Saturday, Sunday and next Tuesday. I have a medical procedure next thursday hopefully will be back on the bike by that weekend. At that point I plan on 3 more rides to the tower, that and a few group rides will get me level 12 and the Everest Challenge, which I should be able to do in the 11 days remaining in the month.
I'm planing on using Zwift in the summer. The bike I have on my trainer is an extra so no hassles there. My biking goals for this year include a century ride and a few big local hills. I'm very encouraged by some of the posts in this thread about how using Zwift in the winter has paid off in the spring.