What your upvotes are worth isn't impacted by what you vote on. What determines what your vote is worth is

• How many times you have voted recently (Your voting Power)
• How much Steem Power Your Have
• How much other people have voted for other posts
• The Steem Price

There is basically a daily fund of Steem that your direct to a post when you vote. If you have more Steem Power your vote is worth more. It's a bit complicated as its a fund that builds up over 7 days.

After HF19 there was a major adjustment to the voting mechanism on Steemit and it has taken a while to stabilise but signs are that we are getting to a more stable level now.