I think you should try it and see how it works out.

I also can't see any downsides except that it may take up more time than you want, but that may simply mean that you read fewer articles and write more comments.

It's possible that if everyone posted explanations for their votes, LW would get cluttered with those comments, but there's no reason to think everyone is going to start posting explanations. Or perhaps the solution would be that an upvote for an explanation is the only thing which doesn't require an explanation-- the upvote is equivalent to "Me too".