well...if all your site's text content is stored in a database, your range of search options/features are a LOT more.

with get_meta_tags(), your searches are limited to what you enter in your meta tags. the problem is, not everyone thinks like you do.
for example, for a page that has details on automobiles, you might choose to use the word "automobile" in your meta tags, someone else might not even know what this means, they might search for the term "car" or "vehicle" which might not be in your meta tags.

if it's feasible and if site searching plays a big role on this site, i think you should look to recoding the whole site in PHP + MySQL.
but if it's just something you want to add on, i would stick with get_meta_tags() because redoing everything will cost you time and money.

if you choose the get_meta_tags() option and it's a small job, PM me and we can discuss how you want to do this if you're interested

actually...it's better if you could email me instead at:
housni[D O T]yakoob[A T]gmail[D O T]com