I could give you a long technically involved answer based on my conservation science background and the material science in question, but I won't subject you to that abuse. Suffice to say, it doesn't matter much (which is why even the experts are so non-committal in their answers to this question) except in extreme instances of high heat and humidity that are going to rapidly damage the print anyway... OK maybe a little more info
The major factors determining your print longevity are your material choices for inkjet paper,inks and possibly coatings combined with the actual environmental conditions, ie., the light intensity on display, the temperature on display or in storage, and the relative humidity on display or in storage.
Picture frame glazing, matting and mounting (which should be specified acid and lignin-free but largely irrelevant whether buffered or unbuffered) goes a long way to reduce the external air pollution effects. Note that some companies marketing conservation quality matt board will have their products also certified with the PAT test (photographic activity test) that is available as a testing procedure at IPI (the Image Permanence Institute in Rochester, NY). It's a worthwhile test for silver gelatin print processes, certainly doesn't hurt and may be beneficial for some ink jet print processes if the matt board passes it.
Any internally generated degradation components from the print itself that would accelerate overall print deterioration are largely out of your control. There are environmental conditions where a sealed package is better than a vented package and vice versa, but unless you can fully specify the environment in which the prints will be kept (e.g. as in a tightly controlled museum storage area) there can be no certain recommendation as to how "sealed" or "vented" your framed print should be. Moreover, without rather heroic measures, you really can't seal picture frames tight enough or vent them well enough to have much of an impact on this aspect of the aging behavior.
hope that helps.
Mark
http://www.aardenburg-imaging.com
