When to start using OSPF

We have 4 offices in different countries. They are all connected via VPN to each other (i.e. at least one VPN tunnel from each office to all other three). Each office has between 1 and 4 separate subnets, and each office has an OpenVPN server. Two of the offices have a DMZ (because they host public services) and each office has direct routing to the Internet. Plus there is one "virtual" office, which is physically at the same place as one of the others, but logically completely separate and connected via a VPN tunnel. In total there are 16 subnets and at the moment this is all done with static routes, complete with failover routes. There are 12 main routers involved.

It all works fine, but I am beginning to wonder whether I should look into using OSPF. Everytime I need to add a subnet, I have quite a job on hand to make sure that all the routing tables are updated correctly.

So I was wondering whether anybody could offer advice on when to start using OSPF for this?

EDIT: If anybody can provide any pointers to a good tutorial or design guide for OSPF areas, I would be greatful.

My 2 cents: I'd setup RIP for a small network like that. Heck I'd use it even if there were only two routers. OSPF is definitely more robust and fully capable of what you're doing, but also more complicated.

My recommendation would be "several sites ago".

Past 3 or 4 routers, statically routing everything feels like more of a chore than getting a route distribution protocol going.