I personally think the advantages of LEDs far outweigh the risks.
We noticed some lamps changing color at Smithsonian American Art and worked with DOE and CREE to detail the mechanisms behind the changes. Our report on color change on LEDs can be found in the link below. Its worth noting Halogen lamps can also change color over time; I am currently having some problems with one manufactures Halogen IR lamps changing color.
The takeaway from this report is that while LED products may not maintain their color quality throughout the claimed life of 25-50,00 hours, most high quality LEDs will last long enough to pay for themselves though a simple payback of reduced utility bills. It is hard to guess how long products will last to museum standards; for high quality LED chips made in the last few months my guess is they will look good for 9-12,000 hours, maybe longer (please see report above for details). The length of payback will vary depending on the utility rates in your region, but saving energy is a good idea just about everywhere.
Lastly, fixtures made with remote source LED technology will likely last their rated life and often come with good warranties. However, track lighting fixtures using remote phosphors are often: more expensive, more difficult to focus into small beams of light and less energy efficient then the competing chip on board LED technologies.
Hiring a lighting designer is the best way to work through these complexities to find good solutions for your particular museum.