I think your idea 2nd method with 6 activities + 2 dummy activities is "wrong", because in your variant it might happen that the 2 dummies are at the first and the last day. So in fact also "consecutive". So you might also add a max 7 days constraint for that 2 dummy activities. I guess this "fixed" method 2 is faster than method 1.
If you ask me: There are so many other things constraints that are more important, you should care about your idea only if you have got an simple data set and all other constraints are successfully added. Don't forget that there are so many things that can affect your "good spreading". Like an ill teacher, an ill student, a public holiday, a project day, ... . In my opinion you will spent too much time into spreading it "too well". Just use a simple min n day constraint and it is fine.
If you ask me: There are so many other things constraints that are more important, you should care about your idea only if you have got an simple data set and all other constraints are successfully added. Don't forget that there are so many things that can affect your "good spreading". Like an ill teacher, an ill student, a public holiday, a project day, ... . In my opinion you will spent too much time into spreading it "too well". Just use a simple min n day constraint and it is fine.