I tend to mash for about 8 hours and haven't noticed any increase in maltiness. I have noticed an increase in efficiency over 1 hour mashes, so there does seem to a bit more conversion after the hour is up. (See also Kai's graphs of attenuation & efficiency for different mash lengths up to 6 hours
Effects_of_mash_parameters_on_attenuation_and_efficiency, but his small samples let the temp drop steeply and his enzymes weren't fully denatured). I suspect my extra efficiency might be coming from the more coarsely ground bits malt that sugars seep out of more slowly. My beers tend to finish 1010 and I suspect might finish a bit higher if I mashed just one hour.
"Malty" seems to mean different things to different people. Some people describe a beer with a high FG and plenty of residual dextrins as malty, though I would call it full bodied. Other people describe the caramel/raisin flavours from medium or dark crystal malt as malty. However, I tend to think of malty beers as those with lots of maillard reaction flavours, e.g. continental beers made with Munich malt or aromatic/melanoidin malt. As Denny said, flavour comes from your recipe, not the mash length.