I have factory Giant SR2 wheelset with 3,000 miles on them . How long before I need to service them ?

Depends on the conditions under which you are riding. Lots of rain, snow, salt, then maybe 3,000 miles it's time.

Personally I probably go longer than I should riding up here with the rain, snow, salt, and road dirt, but I hate doing wheel service, or service of any kind, come to think of it.

What do you mean by service? Are they out of true? Do you clean your drivetrain? If they are true, and the drivetrain is cleaned regularly, you should be fine.

No not out of true . Just started Cycling Jan of this year average 150 miles a week an more . just didn't know if the spoke tension get slack after so many miles or what . U answered my question just didn't know so the only way I know to find out is to ask . Thank you

If you bought the bike new, they may need to be freshened up a bit. As you ride, and especially as many miles a week as you have, things will wear out faster. Brakes, cables will stretch, spoke tension may change, etc. Might be worth taking it to your LBS if you are not familiar with working on it yourself.

I was thinking about servicing the wheel hub.

Check the true. Hand check spoke tension. Braking track. That's about it. If there's a problem take to LBS...or DIY.

True when needed. Cantilever brakes basically don't care about that, mini-Vs seem to be hypersensitive.

I have found that repacking bearings is like better than getting a new wheelset but I don't know how many wheels come with repackable bearings these days.

I replace the bearings in my loose ball Ultegra hubs every winter. About 3K miles.

There's no way that there's an actual answer for this. It completely depends on your situation.

Basically IMO spin them every few weeks and check true on the brakes and see if they're still free and the bearings are silent, eyeball the rims to see if they're getting very worn, and wiggle them to see if the bearings are still properly adjusted. Fix anything you find.

As for spoke tension, IMO as long as the wheel is still true they're probably fine. I do give the spokes a twang and listen. They're somewhere in the octave above middle C for me.

Never.

I use my equipment up as it lives in an urban environment. I consider theft/loss/destruction part of the average lifespan of a product.

I am "green" though and try to buy used items (computers, cars, houses, furnishings to restore) and avoid buying altogether when I can. Thus if I have a part failure (wheel/etc...), I recycle it and just get a used one. I also pay extra to ensure that it's disposed of properly.

Thus, I would run the wheels with no maintenance, as my time is valuable.

What type of bearings do you have in the hubs?

I've always thought of sealed cartridges as disposable. Use them until they're rough, or aren't working for you, then replace.

Lots of variables for loose bearings. Hmmm... that is a good reminder that it is about time to clean and tune my winter bike.

Anyway, for a bike to ride in mostly good weather on pavement, maybe check the cones for adjustment periodically, then clean and re-lube every year or two.