I do inspections for agents and landlords and no, messy isn't a problem. It's 'lived in clutter' and you have every right to live in it! The extremely tidy homes get a much harder look as they sometimes cover up something the LL needs to know about - like the unauthorised dog!!!
Quarterly inspections aren't all that uncommon, it's your home but it is also the LLs investment and, like any house owner, he wants to be sure there are no small niggling things that could turn into bigger things. He isn't checking up on YOU he is checking up on the house. The first questions I ask are "Is there anything you would like the LL / LA to know? Any niggling things, ongoing issues you would like written in the report?"
As for no urgent repairs you can most definitely say no! And tell the agent that you do not give permission or grant access for anyone to enter the house to do them. You can report then to whichever scheme they belong to. LLs should do any and all cosmetic stuff after you have moved out, between tenancies, much as that bothers some of them!
I also do most inspections when the tenants are out, most of the workmen I see do the same. Agents hold keys to reduce the impact on tenants, though tenants do see it as intrusive, I don't think there is a happy medium, someone will always be put out.
And yes, I rented for most of my adult life, so I do know how it feels from both sides!