Having two main titles devaluates it more then it changing hands a bit.
^ is very true. However...
I fail to see how a belt changing hands rapidly devalues a championship.
It really depends on how it's done and who gets it. One of the reasons rapid title changes were done well during the Attitude Era is because there actually were a glut of credible contenders who you could reasonably believe as champions and now there are fewer and fewer of those around so rapid changing of the belts doesn't so much devalue it as much as it's not very interesting because it's always going to the same people.