Hello and welcome,
Funny enough the "issue" is mostly due to over-engineering on Weber's part... The steel bar used on the charcoal grate is such a heavy gauge that the gaps between bars are substantially less than a standard grate. Add in the baskets that have narrow slots running the opposite way and you've more or less removed 60% of the open area from below. Combine that with the use of ash-heavy briquettes (is that the case?) and you will clog up your baskets in no time.
As others have mentioned I would ditch the baskets completely - they really aren't needed in the SCG. They also drastically increase the amount of time it takes to light your charcoal using the burner for the very same reason... there just isn't enough surface area for the flame to hit. Another accessory that will make your life a lot easier is the Weber Charcoal Rake. If you don't already have one I would HIGHLY recommend it to Summit owners and in fact ANY Weber charcoal grill owners. Its made out of heavy stainless steel and I use it not only as a rake but also as a grate lifter and as a mini hatchet to chop down larger pieces of lump. I love the damn thing.
Regarding indirect cooking I have recently been experimenting with different grill setups and found that an excellent option is to actually keep the charcoal down on the lower rack setting, then use the heavy diffuser in place (almost as if you were setup for smoking) but leave one side of the diffuser open so that it lets the heat flow directly up into the top chamber of the kettle. I've had AMAZING results with this setup and I think it has to do with the promotion of circular airflow inside the kettle. The heat races up out of the open side and then circles inside the kettle once it gets up to the lid creating a swirling effect. You could also open both sides and more or less simulate two basket indirect...
One last thing I would highly recommend if you are not already doing so is switch to lump charcoal. First off, far less ash, but more importantly (IMO!)
Briquettes are the hot dogs of charcoal fuel. ... Would you scrape up the crap in an ashtray and roll it back into a cigar? Just sayin'
They sweep up what's left on the floor after making proper lump, add in binders, and then compress it into a puck.
Anyways - stick around and let us know how you make out!
Matt