I actually think a lot of people like to test on tribble regardless of any rewards for it. Because
1) You get to test the newest stuff. New content, sooner then everyone elese!
2) You get to theorycraft about changes.
3) You might even influence how problems and open questions are resolved.
I like all of that. Why keep "grinding" on Holodeck, when there is osmething new to tinker with on Tribble?
I really love theorycrafting and game design discussions.
I like my opinion to be heard by Devs.
Tribble? Yeah, neat thingy. Determining a particular day or week-end for getting a reward? Great way to ensure that plenty of people test the new stuff.