I'm well aware of how annoying people hitting your guild sectors are to the owing guild (I've done it and had it done to my guild). That doesn't change the fact that the behavior you describe could be for some other reason that you describe:
1) Maybe you guys just kill them off so often they grab the power that they can.
2) Maybe they want to harass you.
3) Maybe they want to grab what power they can as cheaply as they can.
4) Maybe they are doing as you suggested: looking for battle points. of course that describes pretty much ALL of GVG.
5) Maybe they think they can run you out of medals.
6) Maybe despite what you think because YOUR the one being attacked and can't stop it (as everyone who owns GVG sectors learns sooner or later) that you want it to be some kind of abuse because quite frankly it costs you far more resources than it does your attacker. Welcome to GVG.
What specifically do you have a problem with? That they attack you every day? How is that abuse? Isn't that the point of GVG (to fight other guilds)? Are you complaining that landing should cost a lot more medals? Sure but then by that standard the rest of the medal cost would go higher as a result and you'd be spending a lot more than 40,000 medals to retake the sector. Are you complaining about the spear fighters? Make a proposal to change that then.....although I've seen posts about that before that went no where. What solution would you suggest? Banning players that attack too much? Complex rules that state you can only attack every 2 days (would that no longer be 'abuse')?
Let me summarize my post to one line: The behavior you describe mimics the normal actions of GVG and to modify that impacts the basic functions of GVG.
P.S. They can't point farm you if you drop the sectors. If you really want you can put spear fighters in for defense and they'll get few points. so if you are correct that it is only the points that they want they'll go elsewhere now won't they?)