As a nearly maxed TH8, should I upgrade my walls to level 8 (skulls)?

Past around TH7/TH8 or so, you're not going to get more loot by leveling your TH up further. You're actually likely to get less - if your TH is a higher level than your enemy's, you'll get less loot from an attack. Thus, from a loot perspective, being a weak TH9 is worse than being a strong TH8. (This statement is true for any TH vs TH+1 comparison, just using 8/9 in this example)

You've got to upgrade your walls sometime, and if you don't do it now, you'll be opening yourself up to worse attacks later on. This slows down your loot rate even further. So neglecting your walls is a double whammy.

Basically, upgrading your walls is an extremely painful process, but doing it before your TH is always the smart choice.

With the frequency of air attacks at your level, it's probably not that terrible of an idea to move on. Despite putting you at a slight disadvantage, it could be worth it for you. I would highly recommend not skipping any research and maxing literally every other building.

It would also probably be way more fun for you, which the point of a game, to be FUN.
Grinding out wall upgrades is NOT fun.

Following @agent86 answer, do know that there will be loot penalties when you're raiding lower TH levels than your current TH level. Meaning, if you're going for TH9, TH8 raids will have a decreased loot, then TH 10 and 11 are the only TH levels left without loot penalties, which are quite tough, and will be harder to raid and loot compared from being a TH8. Check this out.

finish defenses and troops. Do how many walls you can during this period. Them just go tm th9. Its good to start work on your heroes early on considering that they takd more than100 days to max at th9. Dont sit just to max walls.

I would say upgrade or wall maxed and all buildings like barracks resource buildings,hidden Tesla, and all the research even goleam to level 2

by seeing the opinion of @agent86, it is true that leveling up the th to lvl9, will only make the case worse. The walls are provided to protect the village. Even when i was in th7, i did my best to upgrade the walls and then did i procide to th8. The same case was for th8. Upgrading walls is necessary. For even th8 faces air attack, you cant neglect the walls. Like, in an exam if there are 10 chapters, you cant focus on only on main chapters. You have to look after the minor chapters for may be they become you reason to success. But you can still upgrade to th9, because to upgrade th8 walls, it will take 100 days and all your builders will also be idle. Instead, upgrade your th, so that all your walls will be upgrading as well as some new buildings.