The regular train is 2h 33min from Verona to Venice and while this is certainly a let down from the 1:15 or so of the fast train it is still very doable. I have voluntarily decided to take the regular train from Verona because it left sooner even if the fast train got in 20 minutes earlier. I think the train is much easier and more relaxing than any other form of travel and while you will want it to be faster when you're heading home it is manageable.
As for other trips Brescia is city similar to Padua/Padova in size. It also has a very interesting mix of connected city piazzas, amazing Roman ruins which continue in the museum along with interesting art collection and there's castle on top of the hill to explore. I'm apparently alone in this vote but I prefer Brescia to Padova having done both as day trips from Verona.
Lake Garda is very close to Verona (20 minutes by train) and while the lower part of the lake is as touristy as you expect there are some interesting places to visit and taking a bus from Verona gets you further up the eastern coast and out of the train based tourist zone.
Bologna is an hour by fast train from Verona - although the trains are usually less frequent - and is a university town and the culinary center of Italy worth exploring. And at 1:30 on the fast train Florence is closer than Venice will be and is - of course Florence.
My vote is to make at least one trip to Venice - it is an amazing place worth seeing even if it will take an hour or so longer than you expected to get the there. A modest proposal - if you really want to explore Venice go and stay over night for one night and then you'll only spend the extra time on the train there and back once.
I know this is disappointing but Italy has a way of occasionally reminding you that even careful planning will sometimes not save you from the lurking chaos.
Verona is a lovely city and I'm sure you've already looked into but you'll be there in opera season if you want to see an opera in the old Roman Arena or music in the Roman Theater.
Have a great trip,
=Tod