Lindens have no concept of loyalty rewards. The blog on the subject, boasting of sandboxes and furniture made me cringe. Sandboxes are for builders and nekos only. And what is it with furniture as a bonus? Lindens have managed to promote two useless things that cater only to a small minority.
Why can't Lindens think of the bulk of users who come in to play, explore and enjoy SL? A simple loyalty program would be to increase the stipend for each year as a preminum member - 300L- year 1, 400L- year 2, 500L- year 3 and so on.
Couple the stipend increase with larger free houses each year ie 1024 prims after 2 years, up to maximum of 4024 prims after 5 years.
As it stands premium members get very little that is meaningful and as long as techno geeks decide what they think the general user public wants, the premium members will continue to get nothing.