If likes actually meant anything, then the YouTube front page wouldn't be a microcosm of cultural decline.
In the case of an instructional video, it can really be frustrating to watch 10-20 minutes of something before realizing that the maker did it wrong, didn't document it adequately etc. Those videos tend to have a high ratio of dislikes to likes and that can easily prevent one from wasting their time.
I've been doing a lot of home renovations this past summer and watching instructional videos to help guide me. There's a lot of trash out there and it's not always immediately obvious as so without watching for a decent chunk of time. Conversely, there are a lot of videos with low-production values that are highly useful, so judging alone based on ten seconds can be misleading.
There are lots and lots of very niche videos posted by normal people who aren't professional "youtubers" and really just want to help someone out and document things they've done. Video quality, editing, etc. can be crappy, but the information within can be just what you need. Unfortunately there are also lots of absolute trash videos that sort of claim to show you what you need but in the end they don't. Same format. You can't tell which is which before you watch, unless you see that at least half of the thumbs are down in which case it's probably a trash video.
Your use-case was always best fit through the Home Improvement/DIY StackExchange site[0], where an answer is a link to a YouTube video. You can then easily compare different videos, comment and dislike them, and the best videos for that use-case would get to the top of the page.
This may very well be a repeat of Digg 4.0. If we can get the word out that everyone should move their queries from asking YouTube to asking StackExchange, the entire space can be improved over-night. It's all already waiting for us.