I don't mind unlockables if there's a point system like if you need 1200 coins to unlock a character. Anything else is a no for me since I simply don't have the time. 

I don't bother with them because they take so much time to get

I'm fine with any and all unlockables in games, because it's much better than just buying them as DLC, which completely ruins the fun of unlocking things.

However, I agree some are ridiculous, like the ones you mentioned.

I don't see a problem with the 1000 times challenges. Matches usually last only 3-5 minutes. Sure, the time adds up, but if you stick with the game and have fun with it you won't even notice.

It depends on what I get when I unlock it.  So I guess I have a love-hate relationship.

Love them, it gives me a reason to come back to the game and to aim for a goal in which to do my best to achieve it. Sure, I may get sick of it and give up, but after a few days, weeks, months or so, I can come back and continue my pursuit. Then again, I am one of those who obsess over reaching 100%, and even if a game does not require such things, I make up my own goals to reach myself.

It's got to be a nay. They are purely mechanical and don't encourage imaginative, skillful or alternative play whatsoever.

Hate them! They're just there to make people play the game longer, even after it stops being fun. In fact, they could even be said to kill the fun.