The hydrometer reading (more appropriately, SG) won't change significantly enough to worry about. Think about this, at lower saccharification temps, beta-amylase enzyme is more "active" at converting starches to sugars... at higher temps, alpha-amylase is more "active" at converting those same starches to different types of sugars. So, SG is more dependant (albeit indirectly) on the amount of starches than it is the amount of specific types of sugars. Your mash temp just determines what types of sugars those starches get converted to.
As for your statement on higher mash temps, they will produce a less-fermented, "sweeter" beer, but maltiness and sweetness are two different things. You can have a highly attenuated, "dry" beer that's plenty malty.