We can't make that decision for you but just for info: two nights does not net you 2 days -- you'll get one day plus whatever few hours there are after driving there. I stayed 2 nights Oct 31/Nov 1 at Lake Powell at the Wahweap Marina. On the one full day we had we took a boat ride up Antelope Canyon and them lounged around the resort. If you only stay one night you will have a few hours the afternoon before and likely will have to leave in the morning to your next destination. One nighters don't work all that well in the SW because the distances/drive times can be loooooong leaving very little time after you arrive somwhere.

My TR. Short TR - Short trip to SW national parks

Average high in Page is mid 70s in late April. You probably won't need a coat during the day. Slightly warmer in Zion. That's up to you whether you think it's warm enough or if you want to go somewhere warmer.

The weather at Page for a raft ride will be fine, but be aware that the water temperature below the dam is in the high 40's (all year round) so it's not pool/swimming weather if you are rafting. You would want windbreaker/jacket & long sleeve layers for the rafting as it can be cool in the shade. You can always take layers off...

Lake Powell itself will be warmer, but nothing like it is in summer.