Its definitely worth doing when the dollar figure gets close.

Even if the policies are set in stone (about length of service and corresponding vacation days), sometimes they can work around that by given you more credit for years worked at other jobs.

Even when they can't do a thing, its another way to get them to up the dollar figure. For example, when I pointed out an offer had fewer days than I currently had with another job off, the employer offered to give the the difference in unpaid days off if I needed them (until I had enough service to get back to that number of paid days). And then they increased the salary number by that number of paid days to make it net out.

Never took the unpaid days off, just cashed the extra money.