What "I" would do...

1) Wash the walls first, rinse, let dry. If not, you're just priming in dirt/dust which wreaks havoc with adhesion!
2) Caulk the cracks with top-notch product. Let cure a DAY.
3) Prime ENTIRE room, even ceiling.

NOW, 2 choices...

1) Smooth wall - NO texture at all...
* This is WAY TOO EASY to goof up on!! Hire a PRO to do 2 skim-coats and the final sanding.
* Vacuum off all dust. Get out the Shop-vac and filters!
* Don't try it unless you're very practiced!
2) The "Orange-peel" finish. Soft, spatter-bumps look.
* MAY take 2 coats of this due to sandy suface.
* This is also the FASTEST route.
* Once room is taped/sealed off, might take 20 min. to shoot a room (2nd coat may have to wait 1 day).

Now, with your new wall texture, or lack thereof...
PRIME AGAIN!!!
* Lastly, TWO coats of finish-paint.
* If using a deep/accent color, use a tinted primer for that area.

Hope this helps,
Faron

Thanks, Faron...I knew this would be a multiple step process, none of which I want to do, so I guess I'll hire it out. At least now I know what to ask for.

Ceiling is not an issue -- vaulted knotty pine. But room is 13 x 22, with the vaulted walls being 15 feet.

I'll have to bite the financial bullet on this one! :-)

I can already see myself doing a "while you are at it..." for replacing door trim, baseboards, etc.

Have you tried to use a pole sander to knock down the sanded wall texture? Perhaps this will not be as bad as the cost would be to do otherwise. DOn't be afraid to try it first. If it is still too much work or not going well enough, hire it out - find a painter that knows what he is doing - get prices and references - ask for them!