Some random thoughts in no real order (as I'm too sleepy to do this any better!)...
I think you may want to reconsider cards as the first thing you do; you have to be close up to see them, and it's not terribly modular. The scarf vanish can be seen from across the street, is visual, and takes no time.
The need in busking is for tricks that are visual, play big, and are modular; by that, I mean ones in which people can still enjoy when they start watching partway through. Cups and balls or chop cup routines are used all the time for this reason - even if you come right at the end, you can still follow it. The balls vanish and reappear, maybe multiply, or turn into lemons or what have you - even right at the end, people can still get it. Many card tricks rely on seeing the entire routine; without the beginning, the ending is underwhelming. People will keep on walking if they can't follow what you're doing. Coins across, or coin assemblies are good for building the tip, too - even the last phase, people can see a coin go from here to there magically. Of course, it works better with bigger coins, so they're more visible...
The best pitches are where tourists go; they have time, money, and are looking for fun.
You need a polished act; nothing makes people leave your pitch like a flat spot in the show. For this reason, you really, really, really have to tightly script the transitions. You absolutely need to have something to say when one prop gets put away and another is brought out. You have to have a smooth, polished act from top to bottom. Mine has changed maybe six words in three years. "Um", "uh" and a loss for words kills acts.
Pitch the finale, it gives people a reason to stay. Promise them a big, mindbending finale, and do your best to deliver. If you stay until the end of my show, you'll see "something you won't believe, something you can't explain, something you'll tell your grandchildren about".
Be careful about applause before the end of your show; if people applaud, they may feel its safe to go, that they've given you something of value. I don't let them applaud - they can laugh, gasp, yell, anything but applaud. And when they do at the end, it's bigger because they've been holding it in.
Learn some names, and call on them. Make them part of your show.
I do three hat lines; one before the finale, one in the middle of it, one at the end of the show. The first one tells them I'm going to pass the hat. The second one reminds them, and hints about what makes a good tip. The third one thanks them for watching, and puts out the hat. And at the end, have some lines to encourage people to keep tipping. Money is like butter - you have to spread it around to do any good. The more you give, the better I live. Remember, I have a bad back and I walk home - paper weighs less than silver is all I'm saying. Do you need change for a nickel? I really appreciate your generosity, and so does my landlord. That kind of thing. And thank them, shake hands, be jovial, warm and courteous.
If you're serious about it, get some resources specific to busking; Tales From the Streets, dvd by Kozmo, The Royal Touch by Cellini, To Lure With Spectacle by Jimmy Talksalot, and The Art of Krowd Keeping by Gazzo will all serve you well. Watch every busking act you can, not just magic; see how they build the tip, how they hat the crowd, how they structure the show, how polished they are. Busking is a unique venue with its own requirements, so it's wise to look to others for guidance. No need to reinvent the wheel.
Be modular with your show; be ready to stop building and go into the closer as soon as you have enough people. Keep building if you don't have enough.
If it helps, my routine is
One coin routine to stop the first group, start building the tip
Coins to cup
Mongolian Pop Knot rope routine
Hat line #1
cups and balls 1st part
Hat line #2
cups and balls finish
Hat line #3
As soon as I have enough people, it's right to the rope routine and cups and balls regardless of where I am in the set. If I have to keep building, there's a Dean Dill coin assembly i do, a three ball routine, and a mindreading gag.