Learn Turkish: Sence bu eski masa güzelleşmiş mi? - In your opinion, has this old table gotten more beautiful?

The suffix -lAş turns the adjective güzel (beautiful) into the verb güzelleşmek, meaning to become beautiful or to get more beautiful. This is a very common way in Turkish to express a change of state directly from a noun or adjective.

Why did they use the evidential past tense -miş in güzelleşmiş instead of the definite past tense -ti?

Using -miş instead of -ti here implies that the speaker is looking at the result of a process and asking for an assessment. It gives a nuance of asking, Has it seemingly gotten more beautiful based on what we are looking at now? rather than just asking about a definite past event.

Is sence just a combination of sen and -ce?

Yes, adding the adverbial suffix -cE to pronouns creates phrases expressing perspective or opinion. Sen (you) becomes sence (in your opinion). You will also frequently see bence (in my opinion).

Does güzelleşmek only apply to physical beauty?

Not at all! While it literally means to become beautiful, it is broadly used to mean to improve, to get better, or to turn out well. Here, referring to an old table, it implies that the table has likely been restored or cleaned up and looks much nicer now.