Would a lavishly decorated home be simple or elegant?

It would be Elegant. See dictionary.com quote below

lav·ish   [lav-ish] Show IPAadjective1.expended, bestowed, or occurring in profusion: lavishspending.

2.using or giving in great amounts; prodigal (often followedby of ): lavish of his time; lavish of affection.

verb (used with object)3.

to expend or give in great amounts or without limit: to lavishgifts on a person.