I'm actually running my players in 2050 using SR4 rules and the old adventures translated. We just did Mercurial (will eventually be doing BD too).
You *can* use SR3->SR4 translation for characters -- it works, but as mentioned it leaves them a little under-powered, so just beef them a little towards what they're supposed to doing. I'd only worry about those you expect to engage with in combat -- others you might throw some extra knowledge skills to, but unless the characters are going to interact with an NPC extensively, their stats matter less than your ability to give them a personality and bring them to life.
Spoiler contains info on Mercurial...
[spoiler]In the case of Perianwyr (in Mercurial), I actually toned him down a few points from an out-of-the-book Western Dragon on the pretense that "he's a young dragon." A dragon as a human's sidekick indeed! What is this, Pern?
Perianwyr used spirits & concealment, then went after the players at their hideout with the back-up corp police per the book. He fried Max Foley, set the roof on fire, then started peeling the warehouse roof back like a lid on a sardine can. Perianwyr called the retreat when the players used Mob Control on his back-up squad and had a few fire their AVMs in his direction (they missed -- widely). That's when the dragon decided that his employers would not want to risk this special asset trying to get Maria, and he fled. My tactics, but the book made clear to me that Perianwyr was not there in a risk-all position -- that's why the squadron was there with him, to ensure his retreat. Morgan & Perianwyr are still alive to pester the players another day....[/spoiler]
Updating old adventures also works with some help from folk who have translated SR1&2 archetypes to SR4, and the canon SR4 goons, etc. You can steal character stats from real characters from the forums. I haven't had any real troubles.
On the "old style" matrix -- system maps is something SR4 dodges, and it's actually NOT realistic. Within a corporation's system, not everything should be wireless. Wireless is a liability for a corporation. So while SR4 touts that "everything has become wireless" it self-contradicts when it says that most corporations rely on hard-wired systems on-site to keep them from being as vulnerable to hackers. I'd say use the old maps for systems -- note that Scan Nearby doesn't work on a wired network (you may need Analyze -> detect hidden access to another node instead) and only the SANs and perhaps cameras, sensors, perhaps "i/o terminals" (employee commlinks or desk-side workstations).... (and the nodes they connect to of course) are wireless. There's little-to-no reason datastores would be wireless, for example. The CPU is a master-control node, OR if you'd prefer, it could be an executive system &/or honeypot meant to burn intruders?
Some of the earlier adventures have delightful sculpting on their systems....if your player doesn't reality-filter it away.
