I really like the name, but not enough to use on a daughter. It goes in and out of my Top 10. I dislike the Mathea spelling though, it looks really awkward and clunky and would cause me to mispronounce it.
I know what you mean by it sounding trendy, but I don't think it is. I've never met one or even heard about one in real life. I think it's just the sound that might seem very familiar.
From your combos I like:
Mathea
BeatrixMathea
Cecily Mathea
DorothyMathea
Frances Mathea
Gwendolen Mathea
LilianMathea
Millicent Mathea
Miriam Mathea
RosalindMathea
Rosamond Mathea
Rosemary Mathea
Ruth Mathea
Sibyl Mathea
Signy Mathea
Sigrid Mathea
Vivien Mathea
Winifred