I'm on another VB site that does the following method
0-100 : Beginning Member
101-500 : Member
501 - 1000 : Senior Member
1001+ : VIP
Beginning Member, Member and Senior Member are pretty much the same pip, only with different text. The VIP member pip is another color all together and NONE of the colors are the same as staff. :3 I like the idea but I'd like the colors to still be easy to pick apart if that's not too much to ask. ^^ You can give a pip without changing the format of the username, yes?
And if you don't know what a Pip is, it's the only term I'm used to with forums. XD; For me, my 'pip' is my 5 Supporter Emblem...thing. XD Hope it wasn't too confusing.
As far as the spam concern goes, have some faith in the staff people, jee willikerz. o3o They do tend to do their jobs people, they don't just sit around picking their noses. [tho I've heard rumours some staff make homemade flamethrowers out of aresol and matches just to watch people freak out... :3] I just recently had an msn party with someone who hit Senior Member on this other VB forum [we dropped it like it was hot yo, word to your...shiny username? XD;] and it was full of fun for completing the challenge. :D I guess I'm trying to say don't worry about the spam, that's why we have people with shiny usernames who walk around with beat sticks. o3o We're safe~
SO HAVE FUN.