I have also been gradually adding LR and have to say it has been fun. Every other week (payday) me and my wife go to a LFS and pick out a few pnds of rock. As a result we have a very diverse group of rock from fiji, marshall islands and other places. If you have the cash, getting it all at once might be nice but I didn't and I think my tank is actually better for the slow addition. I have been able to pick the cream of the crop when I rock shop.
Trying to get all that rock to look good in my tank all at once would have been a night mare. Not to say I have not rearranged, but it is a lot easier once you are familiar with the rocks and how they 'fit' together.
just my .02