miau -- I like the pokemon ideology of certain "collector sets". There could be certain items if collected together form an power or disadvantage. That's something to think about more. :)
Some of your items are impossible, but others seem like fun promo or ultra-rare, random-encounter items. :)
champ -- "*novelty famicom tshirt - 1 time use, botbr get double chipist points bonus if they win an nsf ohd"
I love this idea, but I think it could be pushed further for example:
"The Famibomb T-shirt". The Famibomb T-shirt has infinite uses. When worn during an NSF or NSF+ OH*, the BotBr wearing said shirt obtains x3 points for a gold, x2 for a silver and x1 for bronze. If a shirt wearer does not make the top 3 during that compo, the shirt explodes, subtracting (vote points x 10) from BotBr's XP. BotBr can drop levels from the explosion. Famibomb shirt's effects are nullified if OH* has less than 4 participants.
SoiledBargains -- That Pleasant Surprise thing could be pretty neat. :D Vouchers like miau said too. :)
Jack -- A jack (from the game jacks, signifying Jack of all trades) is awarded to BotBrs over level 10 who are evenly matched within 250 points between Chipist, Mixist, etc... If a BotBr possesses the jack, the BotBr does not pay for OH*s, or bumping or creating threads. When the jack is lost, such privileges are lost with it.
Alcohol -- Purchased (or stolen) by BotBtown Drunk. When alcohol is consumed, BotBr's view of BotB.org is distorted. For example: Themes, spelling, link order, pictures are distorted until BotBr logs out and logs back in to BotB.org.