I definitely understand where you are coming from.
Keep in mind that for these guilds, you only get to do them once, so the fact that it takes a bit of time shouldn't really be considered an undue burden as much as part of the fun/challenge
The fact is, I really wanted the master builds for each guild to take considerably longer to complete. They are worth pretty serious points, and should reflect every bit of skill that you possess. Even though this is most readily translated into several large building tasks for the Mason's guild doesn't mean that I don't expect everyone to put the same kind of effort and time into the master builds for the other guilds.
One of the nice things is that you are allowed to be in more than one guild at once (with certain stipulations), so if you think the Mason's Guild challenges are too time/brick intensive for you right now, you can always back-burner them to work on another build, or do more faction stuff, like the local challenges.
With the CCC coming up, you can also consider using your Mason master build challenges as a CCC entry, provided you follow any CCC rules for that sort of thing.