So even if i dont get perks past 50 is it worth lvling the skills i didnt get perks in? Does it benefit me?

You do get perks past 50.

Make the enemies harder.

Being a level 81 will make the game harder than it would if your are level 50, so yes.

I have seen no data that supports enemies going past 50. Even the toughest Draugr stops at 45.

You get one perk every time you level up regardless of what level. At least that's the way it should be, and if you want to level those skills, do it, there are a lot of benefits in being good in multiple disciplines even Illusion can be helpful if you put some perks into it.

depends on the skill, but for the most part, no. skill ups are now mainly just to give you access to better perks. leveling mage skills is supposed to reduce the cost of spells, but i never saw any notable difference. i dont even know what leveling weapon skills or crafting skills is supposed to do...

you do still get perks though, so there is reason to keep leveling up.