You probably already know all that, but it's a good warning for anyone. If you're going to a convention and plan on getting a lot of StreetPass, you HAVE to check your Plaza very often!! Otherwise you'll max out and not only will you not be able to get anyone else's StreetPass data, but they won't be able to get yours, either! Try to check your Plaza every 15-30 minutes at least.
I believe I was at Disneyland a few months back, and while I didn't get 100 Streetpasses that day, I got well over 40-50. Since I was also holding my sister's unit while I was there, I did a similar system on checking my Streetpasses out of necessity:
1.At around 5-6 new Miss, I checked the plaza, swapped pieces I needed, (and if I had time) played through Mii Quests I had going on.
2. Switched units, while still in the plaza getting hits on my Streetpasses, and brought down the number on that unit.
3.Repeat, and if you get on an isolated line/area, check your other games too! (I prioritized Mario Kart and a couple others.)
Also, for anyone who finds it very inconvenient to have to pull your 3DS out of your pocket every few minutes at conventions, here's a little thing that I do that has worked very well for me. If you have a Circle Pad Pro wrist strap for your 3DS (or a Wii Remote wrist strap), you can just strap your 3DS to your wrist and hold it or just let it hang their. *skip a little* It's also an easy way to let other 3DS owners know that you have a 3DS.
I do the same. As I have found with my own (relatively new group) in the area I live in, many of the 3DS owners are in fact, kids, and cannot make it to the events. Despite this, when they see me with my 3DS while I am shopping, they ask if they can Streetpass, and I am happy to let the machines do their thing (and tell them to keep the wireless on, as they, and my 9 year old sister tend to turn it off when they play or whatever).
I am also finding people around the demo kiosks too. They get their tag from the machine, and from mine, if they hang around for a bit too! I figured on how to access the main menu with most of the demo units, EXCEPT the new ones with Mario Tennis (it used to be hold select-start-L-R at Startup with other games that you couldn't just press home button on, but this game...it doesn't work. I'll figure it out =p)
Oh, and to pimp my own group (If allowed), I shall link to one of my series on tips and tricks to the Mii Quest 2 secret path
Here. I plan on doing more of these very soon, but suggestions are welcome, if you guys have any too!