You are not alone! And I think the points you've made also uncover why new users abuse the "introduceyourself"! I made two introduceyourself posts, and the second was just because my first wasn't that great. I left it thereafter, yet I there are multiple posts in the intro by the same author(s), and some are shameless snake-oil marketers that deserve downvotes, so they should be discouraged from cluttering this important section.
I see no wrong in upvoting your own comment, especially if it is buried in a sea of comments on a popular post! Some people leave "gold nugget" comments there, with good links even, but they get overlooked because "0.00" is beside them.
I completely agree with you about the abuse of the introduceyourself tag! Whenever I browse through it to welcome new users, there is so much crap there that's not about an introduction at all...
Yes, I think sometimes upvoting your comment is needed if it holds important information in a sea of other comments. People argue though that it's up to others to decide whether it's relevant or not, but on a very active post, you can very quickly sink to the bottom, without ever getting a chance to be seen. That is kind of frustrating and it has happened to me a few times aswell.