Sorry to be a bit slow but I wanted to poke around a bit. Yes, I think this is closer that Paul Blay's 2008 submission.

@@ -12 +12 @@
-<gloss>an overactive imagination</gloss>
+<gloss>(having an) overactive imagination</gloss>

妄想	4721576	98.7%
妄想癖	61564	1.3%


https://ja.wikipedia.org/wiki/アカネマニアックス〜流れ星伝説剛田〜
https://en.wikipedia.org/wiki/Akane_Maniax
剛田城二（ごうだ じょうじ） Japanese wikipedia
妄想癖があり、茜に罵られる事も多い。
Jōji Gōda (剛田城二) U.S. wikipedia
He has a tendency to lose himself in his imagination,...

======
One person's translation:
Practice English with Marilyn Monroe "Skirt Scene" 　マリリン・モンローになりきって音読
https://www.youtube.com/watch?v=UHzti6Yt1NI
Richard is a faithful man, but has an overactive imagination and faces a mid-life crisis. While his wife and son are on vacation, he meets a girl (Marilyn) who is a commercial actress. 
リチャードは誠実だけど妄想癖があり中年の危機に瀕している。

＝＝＝＝＝＝＝＝＝＝＝＝＝
There is no 1-1 match here, but you can see what kind of personality is being described
https://ja.wikipedia.org/wiki/アンジェラ・アナコンダ
https://en.wikipedia.org/wiki/Angela_Anaconda
妄想癖があり...
The majority of these feature her rivals Nanette Manoir and Mrs. Brinks, seeking vengeance on them in unrealistic fashions. Angela often imagines unusual things happening to her enemies, especially Nanette, including getting tossed into the air during an ice routine and falling through the ice, or getting turned into a flash card, among other things.

====
https://ja.wikipedia.org/wiki/あつまれ!ふしぎ研究部
高浜 麗子（たかはま れいこ）
南湘高校2年。不健全な妄想癖のある風紀委員。
vs:
https://atsumarefushigi.fandom.com/wiki/Reiko_Takahama
Personality
Reiko is a girl that always sees everything as lewd. She always calls everyone indecent and always thinks that others are doing lewd things in every situation.

Usage (among others): 妄想癖がある人 : a person with ~

Literally, "a tendency toward fantastical/made-up thinking."

The *癖 entries are habits and tendencies, not people. This entry stood out.

I discussed this with a Japanese woman, mid-20s, who said the term is super common. "delusion" would be far too strong.  The term is used frequently to describe the personality traits of characters in anime/manga/etc.  (I can see this on wikipedia listings for various manga that give character summaries).

I can find no apparent translations of this term online.  After a lot of work trying to match up Japanese wikipedia articles that had *anything* like the equivalent, and reading a bunch of parallel character descriptions without literal translations, I thought of "overactive imagination".  My Japanese correspondent said: "過活動の想像…yes perfect one". 

I think the article [an] is needed for comprehensibility (usually as: a person with ~).

I don't think this is especially [col], and I think it has ample descriptive use that it's not a sensitive term on its own.  Obviously you can use it as an insult, but isn't anything like a slur in isolation.  Japanese correspondent said she'd have no trouble using it to describe her self at times (not that this excludes it from being sensitive).

@@ -12,4 +12,2 @@
-<misc>&col;</misc>
-<misc>&sens;</misc>
-<gloss>day-dreamer</gloss>
-<gloss>fantasist</gloss>
+<gloss>an overactive imagination</gloss>
+<gloss>tendency to get lost in one's imagination</gloss>

Entry created