130mm hub on 135mm frame I'm looking to upgrade the wheels on my touring bike to a lighter set of road wheels. The frame is aluminum.  According to Sheldon Brown you should be able to just put extra spacers between the locknut and cones and that's it. Apparently only  2 or 3 mm  sticking out past the locknut is enough to to properly secure the wheel.  

Is the above procedure really advisable? Would it be a better idea to take the existing 135mm (146mm actual) axle from my existing wheel or would it make no difference and I would be better off not doing such modifications to a new wheel? 

The reason I'm thinking of doing this is because all the 135mm wheels I've found seem to be disc brake wheels, and the rims have no braking surfaces.  The only other option seems to get a custom wheel build which will bring up the cost of the wheel quite a bit and basically eliminates the ability to buy anything at a discounted price.
The QR (on the outside of the dropouts) and the locknuts (on the inside) are what hold the wheel in place - you could have the axle ends flush with the dropouts and it should be fine (Sheldon describes this setup somewhere, with only the skewer going through the dropout, to allow perfecting chain tension on a fixie with vertical dropouts) - but 2mm axle projection vs 4 or 5 makes no difference. Definitely DON'T "spring" an Al frame to fit a hub of different width - generally ok with steel if it's only a few mm. If you want a wheel that's not available off the shelf, don't be afraid to build your own - it's really quite straightforward, again SB has the clearest instructions I've found (at least, they were what I started with) and you will very likely end up with better wheels for less money that a factory wheelset.