I know you are not ready to list, but have you talked with any Realtors. I would discuss these questions with them, also check for any open houses that are similar to yours.
I do think you want your house to look up to date, I think 15 is about the worst age, getting old, but not really needing updating, but the buyer wants up to date.
I wouldn't paint your cabinets plain white, look for a softer classy off white.
Replace all the blue, but think hard about the right color, you want up to date and classy.
Replace brass, shows dated.
I'd probably replace the doors.
Will you have as much leaves in the spring? If so, hire the gardener.

Oh, I forgot one thing, can you add more slate to make it all slate? Slate is popular now, that would be a good feature.

Assuming I could still get the same slate...would cost about $12k most likely...more than I want to pay for just one thing. With the blue cabinets in the workroom/office any thoughts of what color to paint...the granite is bl

5. Bathroom has brushed chrome fixtures. Doorknobs are brass. Replace?
Brushed chrome is fine. No one is going to notice that the doorknobs are brass. Cheap shiny fake brass chandeliers are what date a house.

6. I would love a keypad locking door.

7. If you can afford a yard service, that's great. Drive up appeal is important.

Talk to a few realtors before you do anything. They will have a better idea if the blue needs painting over. I know a friend of mine just sold a house with a lot of blue and she told me they got several comments about there being too much blue, but it still sold. However, hers was an inexpense house, I think people expect more from expensive houses.

I wouldn't worry about the chrome fixtures. Ask the realtors about the brass doorknobs. Leave the keypad on the side door, ask the realtors about the fingerprint locks.

If you can afford someone to keep the grounds in good shape it will be well worth it. If you sell in the spring there shouldn't be any brown leafs to rake but you need to keep the property very neat.

A house in the upper price ranges will attract buyers who will plan their own remodel of the kitchen and bathrooms. You want them to look clean, nice and functional for selling so the buyers can move in a do remodel on their schedule. Redoing floors could be in that same category.

Repainting to a neutral attractive color would make sense.

Keeping the yard well raked would be huge in my opinion. If it looks like a lot of raking is involved with owning your house, people will cross it off their list.

I liked sheliajoyce's comment re the repainting to a neutral color, other than that I'd spend my time and energy on making sure everything is neat, uncluttered and CLEAN. People can see past the different tiles , door color etc . but dirt and clutter, not a chance! Of course, I would assume that there are no surprises in store for a prospective buyer, such as a stove that doesn't work, leaks etc etc.

Speak to several Realtors very familiar with your market to pick their brains. If you are upper end people will expect more. This will include new appliances and fresh, neutral paint. The floors are tougher and where a local Realtor's opinion would come in handy.

You may want to hire lawn care for once at least week with additional weeding, pick-up-sticks duty. Our lawn guys do additional work for us every week, but remember they aren't gardeners. We did have gardeners for two years and the gardeners were twice as expensive as the lawn guys. For your purposes, the lawn guys are more than adequate.

We have a key pad lock on one door. Next house, every door will have one! Leave the key pad they are fantastic (we never use a keyed entry anymore).

How hard would it be to match the wood that you currently have? What I'm thinking is you could remove some of the brown tile and create a wood border around it if the wood is also visible in this area. This would create a break between the two tiles and would make the entry have a more custom look.

Thanks for comments. I will talk to local realtor before finally deciding on things. Having said that, we looked at a lot of houses when we were buying this one so I have a good feel for the area. Having sold a couple of houses previously we know to declutter and keep the house spotless and on the last two houses we repainted and recarpeted. We will replace the oven and cooktop in the kitchen...something not really high end but adequate enough that any buyer would feel comfortable using it until ready to remodel.