There are any number of valid reasons to cover the boat and only one, albeit not so valid, for not covering it.
How you choose to do it is the better question - tarps are the cheapest and most prone to coming loose with sometimes consequential damage resulting. It's not a good idea to attach anything to the lifelines as they are not designed nor intended to carry the substantial snow load which could result. A frame may be more work but as is usually the case, anything worth doing is worth doing "right".
You can have a custom made cover done although too late for this season for far less than you might think and particularly so if it is only a boom tent cover.
My theory is the extent to which one goes in covering his boat is directly related to how much he likes it.