I'm not sure if AA will let you buy back PLT status if you previously held it via Challenge only. In other words, because you did not qualify "for real" in 2004 with miles/points/segments, you might not be eligible. You should call AAdvantage Customer Service (1-800-421-0600) to double-check.
If you are eligible, then consider these issues:
1) Is most of your travel mostly domestic or mostly international? If your travel is primarily domestic or "North American," you won't benefit as much from the lounge access policy. Also, unless your O/D is a major hub, you still will be able to use F-class check-in if you drop to GLD.
2) Are you planning to requalify for PLT this year using miles/points/segments? If so, will you fly those early enough in the calendar year so that you won't be without PLT status for very long after March 1?