哇，貌似从来没想过这个问题。应该都是一样的。 美得多，美多了，都是一样的 不过如果是动词的话，可能会有点不一样，比如，吃得多和吃多了

Believe me, there's no any difference between them.Just as you know,the Chinese is a very flexible language and there are several means to express the same meaning.And also there's no difference in the attitude and the tone. hoping it can help you.

Cute question. In the case that you gave (a monosyllable/bisyllable adj.+得多/多了）, there is almost no difference of meaning between them. Actually, ...多了 is the elliptical form of ...得多了, and the full form can be seen in some writing. The reason why the 'de' is ommitted in daily use is that modern Chinese has an inclination to make syllable sequence in double or foursome. As you read more and more, you'll find this insteresting law in Chinese, and this(prosodic or rhythmic laws) will explain many subtle phenomena in language.

在您举的例子中，意思和用法相近，都表示一种程度。 不过“得多”一般用于形容词和副词后； 而“多了”有时可以用于数量词之前，比如，“多了一个人”，表示数量上的差别。

but in other cases, it might be subtle difference between them. for example... 他比我喝得多 and 他比我喝多了 （when two guys are drinking....）the first example only means that he drank more than me, but the second one imply that he was drunk.