Just lately many big maps were being made, I was making one too. I've experienced problems with SVG file size cap, as a few others map builders. This is really annoying - do a lot of work, just to realize that after 80% of map done you have to redo it or decrease its quality. And not to mention that if you're using polygonal chains, not curves, to draw territories, then simplify tool won't help you.
Fizzer suggested using SVG file optimizer. There is actually one named scour built into new versions of inkscape, so I've tried it. At first it was great - 25.2% size drop after using it. But. The file was unloadable. I've been receiving the message that the file has some parameters in other units than px and warlight accepts only px. Then I've did it again but un-checked all the possible options (guessing that one of them is responsible for that). The result was loadable, decreased in size file... But again, it looks like that:
Well, you can say that my map turned into porcupine. But I wouldn't be writing it if I haven't found the solution, wouldn't I? It is even simpler, and it was always there. You just have to "save as" pure SVG file. I'm not sure if it's named exactly like that, because I have polish language version of Inkscape. It's the second option just below "save as" Inkscape SVG.
Size drop is 18.8% in my case. Thats not 25.2%, but hey, that's still pretty much for something just as effortless as that... and it's completely safe for the file - I've checked it. No porcupine here.
Keep this up and post here any other effective, fast and safe methods to reduce your file size if you find any. Good luck in map building.