Yes higher mash temperatures can be utilized to get a maltier beer. If you're in the 155 range when malting though, I would suspect that this may not be the issue as much. You don't want to go too high (like above 162) as you'll denature the enzymes needed for conversion. Have you checked your thermometer to make sure it's accurate? Test it in boiling water to make sure it reads 212, if not you may be a few degrees off on your mash temperatures.
There are other things to look at as well. One is your recipe. In order to get malty character and a fuller body, you need some unfermentable sugars in your wort. If your recipes are lacking in crystal malt, or you're making mostly lighter colored beers you may not have enough of these types of grains to add any substantial body.
Are you using the same strain of yeast to ferment all your beers? This could be another culprit. Some yeast strains have a higher ability to attenuate than others, and some are better at fermenting longer sugar chains like maltotriose that other strains leave in. Are you getting a lot of attenuation on your beers?
Basically what I'm saying is there are many methods to get a maltier beer with more body, but mostly the way to get there is to have some unfermented sugars left in your beer. Maybe a walkthrough of one of your brews, complete with mashing schedule, recipe, fermentation level, how you carbonate, etc would help determine what will work best for you.