Well, if you accept that downloading client is legal even if you are not in Beta, you can also make some "little" modifications to actually watch replays you want..
There is way to import maps what you are missing.
Here you can download maps what you are missing.. importing it into cache is another story but nothing where you need to be some sort of hacker..
For example, look on Lost temple map..especially file name.. just numbers and letters. What you need is create few folders in
c:\Users\yourname\AppData\Local\Blizzard Entertainment\Battle.net\Cache\ (windows vista/7).. folder names have to be first 2 characters from file name. For lost temple is 93.. than you need create another subfolder which will be another 2 characters from file name..again for Lost temple is 9a .. so full path will be
c:\Users\yourname\AppData\Local\Blizzard Entertainment\Battle.net\Cache\93\9a and here you will put the map.. now you should be able to watch every replay played on map Lost Temple..