I think replies to my own comments are actually easier to up-vote than comments as I'm browsing them. Generally, my rule is that if you reply to me and tell me something new (i.e. not just agreeing), you get an up-vote. If I'm replying to you, you (and usually everyone above you) almost always get an up-vote. After all, you got me to reply (something I don't do with very high frequency).