I will admit I've regretted votes at times (voting lower and then wanting to make it higher), so it sounds a good idea...
...until you consider that, alternatively, you can make sure you cast your votes carefully. You don't have to vote once the beatmap ends. If you're not sure, don't vote and come back later. In case of a difficult beatmap you don't feel like playing to the end again, you can vote at the beatmap's page in the Listings. The permanency of votes can encourage players to think before clicking.