That would certainly be a great bot, but to be able to "[leave] free random upvotes worth a great deal" you would need to have a LOT of Steem Power. Typically bots that have a lot of steem power pay a lot to lease it so they need to charge for using their bot.
If you get a great deal of SP and want to give out free upvotes i'm sure everyone would love you for it! If you do that and want a bot for it let me know and I could code it for you pretty easily.
Thank you, currently messing around with Heroku learning all that... Looking to supply it with about $75 a month of steem to power it up and keep making its vote worth something.... This thursday will be its first purchase of steem, currently donations are accepted which allow me to add people to the whitelist on Heroku, no matter the amount.
I just need help programing on how to let it vote 100% every 2.4 hours, just goimg down its whitelist in order, leaving presents....
I set up @poweruprewards so that eventually it will be a free upvoter that only accepts donations to keep the steempower climbing.