You can always manufacture cap room. There is just a price to pay for that eventually. And players and their agents know that, too.
Belichick has always been smart with the cap and has never left them in bad shape going into coming years but they have much more leeway now than ever before because of the expected rise in future caps. They have major re-signs coming down the road but even with that taken into consideration they really have the opportunity to be aggressive if they wish to be, and imo they should be because the rest of the league is going to use that impending space to better their teams and the Patriots should be doing the same. As always it will come down to value but iif they see it there they should go for it because the room to absorb those contracts is going to be there. They don't go big in free agency often but they do go for it every now and then, albeit with mixeed results, AD being the major bust. That shouldn't, however, keep them from going for it again if they see an opportunity for a truly great player. I have no idea how Belichick sees Mario Williams but if he feels he is a player that can be a big time game changer on defense then I would love to see him take the plunge and go for it. They could still get priced out of it easily by a team like the Skins who doesn't take anything into consideration when throwing money around, but if they can get it done within reason i would love it. I don't think their defense is "a player away" by any means, but i do think a true game changer could take them to a much higher level, and they can fill around them with this draft. A pipedream, most likely, but it's a day before free agency, i can dream.