If the original poster is mainly referring to his photo collections I would assume he has some sort of photo catalog / editing software. Some even come free with the camera. I know for sure that Adobe Lightroom keeps a very extensive catalog of photos imported/edited there no matter where they actual fle is stored.
This locally saved catalog allows for very detailed searches within the EXIF data, as in: "show me everything taken between April 2009 and June 2009, labelled church, dimensions not below 1024x768 and take with my 24-70 lens" etc.
If this is the functionaliy the OP is looking for the answer is not overloading a NAS with features only a minoriy will use, but rather investing in the software by himself.
And from my understanding of things a remotely (on the NAS) kept index of files would have to be all compatible with the SAMBA implementation on the Windows clients. From what I know the current versio of SAMBA on liux only include the most important features. On the other hand, a repeatedly updated local (client side) index service is kinda of pointless, because in a lot mof cases multiple peple have access. So if the client relies on the local index whic might be outdated, it might deliver false results. Or it would have to update so ofter that it becomes a terible ressource and bandwidth hog. To make sure a file you look for is there or not on the NAS at the time you look fo it, the NAS has to scan it from A-Z to deliver a reliable result.
QNAP TS 509 Ultra (E5400 @ 2.7GHz - 3.5GB RAM - 5x3TB Hitachi, soon to be back to Samsung 5x1.5TB RAID5)
Synology DS1812+ (stock with Hitachi 3x3TB now, soon to be Hitachi 8x3TB RAID6)
Fantec QB-35US3R dumb RAID case (USB 3.0 / eSATA / Samsung 4x1.5TB RAID5, soon to be Seagate 4x2TB RAID5)
Lenovo Thinkpad x220t Tablet / i7-2620M @ 2.7GHz / 8 GB / 128GB)