Why wouldn't you just replace the valve seals? Replacing the valve guides
and seats seem like a very expensive option. If you are going that far, a
rebuilt cylinder head might be more cost effective.

That is the symptom usually associated bad valve seals. I just don't think
that is normal for any modern engine, especially one from Toyota that has
been properly cared for. However, almost any engine that is burning
realtively samll amounts of oil will mimic the "smoke only at start-up"
symptom these days. When the car is cold, the catalystic converter is not
effective. However, converters heat up quickly, and once they are in
operation, they'll take care of quite a bit of oil smoke. I'd replace the
PCV valve and make sure there are no external leaks. Unless the problem is
related to these items, the repair cost is likely to be high. You can buy a
lot of oil for what valve seals will cost. I also suggest you carefully
monitor the oil consumption over a longer period. Over how many 500 mile
periods have you noticed the higher oil consumption? Warm weather and long
trips can mislead you. See the following references:

http://www.pzlqs.com/Tech/Bulletin/QuakerState/General/pdf/g11.pdf
http://www.pzlqs.com/Tech/Bulletin/QuakerState/General/pdf/g11.pdf
http://www.pzlqs.com/Tech/Bulletin/DomesticMarketing/General/pdf/g01b.pdf

If the there are no external leaks, and the PCV valve is OK, then my next
step would be to try one of the high mileage oils, and possibly go with an
oil of a higher viscosity. Paying for valve guides and valve seats would be
a lot further down the road for me.

What brand of oil have you been using? I know it seems to be unlikely, but
years ago I had a car that appeared to use more oil when I used one
particular brand of oil (supposedly of the same viscosity).

Ed