the system as it is right now doesnt take away all your remaining vacation days at the end of the year ... it fills them back up to 30 day on the first day of the next year.
plus, as bbw said, you can renew early. my membership runs out at november (i think), when i renewed i was back at 30 days again, and i will be back at 30 days again in january (minus the 5 which i will spend on the very first 5 days :))

just use the vacation days when you need them .. try to be clever with your weekend days, and use automatic vacation days for unknow situations :)

the 'days per month' solution is pretty bad when you first start, as you will start with only a few days. this will even out when a couple of months have passed and you saved up enough. if you are above 30 days it should not add more (otherwise someone could hoard 100s of vacation days and abuse those ;)) .. which would make no difference with the end of the year as it is right now

for me the system as it is right now is the most flexible system there is .. as long as you keep yourself in hand just a little tiny bit and save some for later :)

automatic vacation: its like BBW said, i know from experience.
when a game times out and you ahave automagic vacation days set, then 1 day will take from your total vacation days and the game wont time out. that day is now counted as a vacation day for any games which would time out on that same day
(it doesnt add 24 hours to all of your games though)

the fact that it doesnt add 24 hours to all your games make the difference between fixed vacation days and automagic ones ... when you are sure you will need a certain day as vacation day .. set it as a fixed day! .. that way all your games will profit from it by having 24 hours added to them