I try to give my kids time away from each other, and let them do activities that don't include their siblings regularly. My mom kept my sister and me in all the same activities growing up, and it meant that we were always treated as a unit, instead of as individuals. We are very different people, and if we'd been able to choose something just for one of us, and not the other, I think we would have both been happier. For example, my sister loved soccer, so my signed us both up for same team-- I spent all my time gathering dandelions, and my sister was treated as a less capable player because of it. Also, it exacerbated the sibling comparison/rivalry issues-- we couldn't do anything without knowing whether or not our sister was better at it. And we weren't homeschooled, so we were separate all day at school.
As a homeschooling family, my kids get lots of time together, and so I think it's even more important that they be allowed to be apart sometime too.
Re: drop-off parties. I think drop-off parties are MUCH MUCH easier to host than ones where the parents stick around and need to be entertained too. Most people I know who do drop-off playdates are happy to reciprocate, so it's not treating you like you're a daycare, it's parents helping each other out while their kids have fun.