So this is just an opinion. I'd still be using 2007 if it hadn't been for a pc loss, but then again, I'm not building for anyone. Older db's can have issues opening newer ones because of unsupported features - many of which are often not required. but anyone who has a newer version should be able to operate anything you build in an older version. One of your drawbacks is that you don't know how it looks when it gets 'transformed' by the newer version. Then some will say that by not upgrading, you expose yourself to some liability because older versions are no longer supported by M$, so any issues caused by vulnerabilities become your problem. Aside from any technical concerns, how will your potential customers view you as a prospective supplier if you fail to upgrade? They might consider this to be an indicator of your seriousness, to say nothing of what concerns they might have about those vulnerabilities.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.