The OED specifically traces the term "dirty money" to a source over a century old:
dirty money (n.)
1897 S. Webb & B. Webb Industr. Democracy I. 313 When any class of work involves special unpleasantness or injury to clothing,
‘black money’ or ‘dirty money’ is sometimes stipulated for.
1960 Sunday Express 14 Aug. 1/1, 1,100 dockers‥are claiming ‘dirty money’ for handling a cargo of red oxide.
Yet for some time, dirty has been applied to more than our dirty socks, or a muddy shirt. Dirty has been used to convey sullied, tainted, impure, corrupt, illicit, immoral, etc.
The OED lists such nuances among its several meanings for dirty:
2a. Morally unclean or impure; ‘smutty’. Spec. dirty book, a
pornographic book; so dirty bookshop; dirty joke, dirty story, a
‘smutty’ joke or story; dirty weekend, a sexually illicit weekend.
2b. That stains the honour of the persons engaged; dishonourably
sordid, base, mean, or corrupt; despicable.
1764 Pulteney in Beatson Nav. & Mil. Mem. (1790) I. 26 Some Ministers‥cannot do their dirty work without them.
With that kind of heritage for the word dirty, it's not a long leap to apply the word dirty to ill-gotten funds.
As a side note, in addition to dirty money, the OED doesn't forget or neglect dirty pool, dirty words, dirty tricks, and dirty old men.
Expensive is behaving as a typical adjective, which are only modified by preceding degree words, e.g.
It was more expensive than...
It was more sudden than...
It was more amazing than...
If we pretend for a moment that is worth was a verb, we could compare it with some other verbs of measuring activites, e.g.
It weighs more than...
The room seats more people than...
It measures more than...
It costs more than...
The phrase is worth behaves likes a stative verb. The only other comparable phrase I can think of is [be] up/down as in:
The Lions are down three points.
The Lions are up more than the Bears were up at this point last week.
If worth is an adjective, then it is one which is almost always restricted to being a predicative adjective. This is how Oxford English Dictionary (OED) describes it, noting that it is used
Almost always (now only) in predicative use, or following the n. as part of a qualifying phrase.
What is interesting is that although an expression like
*Gold is more worth than silver.
with a preceding degree word, would be usually considered ungrammatical, there are several attestations listed in OED of exactly such a usage (where a degree word precedes worth) from the Early Modern English period:
1568 Newe Comedie Jacob & Esau ii. iv. C iv b, Ah sir, when one is hungry, good meat is much worth.
1581 G. Pettie tr. S. Guazzo Ciuile Conuersat. (1586) iii. 138 It may rightly be saide..that the feathers are more worth then the byrde.
1615 W. Lawson Country Housewifes Garden (1626) 6 Fruit blown vnripe, are small worth.
I'd say worth is an unusual word, and has only become more unusual in recent history.
Best Answer
[CED]
(though see the caveat at Better than premium)