I understand that can be frustrating, but as you mentioned part of that is by design. Stack Overflow gets its success by being laser-focused on questions and answers, to the extreme that comments like "thanks" are seen as noise for developers to wade through to find the answers they are looking for. That's why they have such a high bar to comment - the number of "thanks" and "this solved my problem" comments would be a staggering moderation issue. Either that or the site would turn into a long-winded discussion forum.
In short, only questions and answers add any real value to the site for the most part. If you really want to contribute to the community, consider diving in and writing questions and answers.
As for upvoting, I understand that it's frustrating not to be able to vote in a community that you spend so much time in. But on the flip side, realize that 90% of the value of Stack Overflow comes from its questions and answers. If you want to contribute to the site, it only takes 3 upvotes across all your questions (or 2 across all your answers) to gain the upvote privilege permanently.
In short, only questions and answers add any real value to the site for the most part. If you really want to contribute to the community, consider diving in and writing questions and answers.
As for upvoting, I understand that it's frustrating not to be able to vote in a community that you spend so much time in. But on the flip side, realize that 90% of the value of Stack Overflow comes from its questions and answers. If you want to contribute to the site, it only takes 3 upvotes across all your questions (or 2 across all your answers) to gain the upvote privilege permanently.