Does the word "extravagance" only have negative connotations?

Solution 1:

I think you could probably wrangle extravagance to not be perceived as negative, but it will be hard. You're right that it does often carry at least mild overtones of negativity and judgment. However, extravaganza, a closely related word which could work here does not. So you could say:

A melodic extravaganza.

Extravaganza is defined by the online Merriam-Webster dictionary as:

Definition of extravaganza

1: a lavish or spectacular show or event

2: something extravagant

3: a literary or musical work marked by extreme freedom of style and structure and usually by elements of burlesque or parody

Note how the third definition given is very close to what you're after, albeit without the element of parody. Also note how the definition of extravaganza lacks the negative connotations implied in the same dictionary's definition of extravagant:

Definition of extravagant

1. a: exceeding the limits of reason or necessity
   extravagant claims
   b: lacking in moderation, balance, and restraint
   extravagant praise
   c: extremely or excessively elaborate
   an extravagant display
   

2. extremely or unreasonably high in price
   an extravagant purchase
   

3. a: spending much more than necessary
   has always been extravagant with her money
   b: PROFUSE, LAVISH

4. a archaic : WANDERING
   b obsolete : STRANGE, CURIOUS

Solution 2:

I sometimes say, "I purchased something fancy, it was an extravagance, and I am excited." Thinking about it, the word does have some negative connotations. But I think they come from context rather than the word itself.

I'm not familiar enough with Latin to speak to the root of the word.