You and I sound very much alike (meant to go to original poster, not sure who I am commenting too lol). My office is actually very inviting. I have pictures of the kids on the wall (they love that), things they've colored me in frames on the walls, its very colorful and fun. I have books that they can read that are "nursing" such as doc mcstuffin books or informative books about ear infections with pictures for the older kids. I am a KG-4th school nurse and I don't think rewards make your office a place to come and hang out if you are stern with your nursing visits. If they come in for something serious, I take care of them. If its something minor and they are older (2nd through 4th) they get the care they need, and sent back to class. If I can tell they need a little bit of positive reinforcement or just a listening ear because they are having a bad day, I will give them something to cheer them up. If they are brave after being injured or do something kind, I reward them with an incentive. I think positive reinforcement goes along way with these kids. My older kids don't care about stickers or things from the "treasure chest" they'd rather just have someone to come talk to. I am that person, and happy to be.
As far as ideas - I have stickers right now but LOVE the kiss stamp idea! That's sweet. Also every time they loose a tooth I have printed teeth and write their name on it outside of my office in the hallway on the "look who lost a tooth" wall. They love this, as well.