Let us do something else, let's increase the number of word classes, and let us do that by splitting the adjectives in two!
How would one go about doing something like that? First, let us make them behave differently morphosyntactically; have one of the classes mark congruence with the noun as far as case goes. Let us have the other category redundantly mark some kind of noun class system along the lines of the system of Chinese.
Let's call the two adjective kinds adjectives and adjectoids. The difference given above seems a bit small, let us come up with some other differences, both notional and syntactical.
A simple difference that could be relevant to the speakers of the language would be whether a word is understood as denoting that the noun has a quality, or denoting that the noun is a member of a class with a distinguishing trait.
- mark case and number
- productively can form verbs both or 'turning increasingly x' or 'make something x'
- use location-like metaphors (go (to) x, g from x, stand at x)
- have case-congruence even as verbal complements
- come closer to the head noun
- mark noun class
- tend towards more periphrastic expressions
- use membership-like metaphors (join x, be of x, be with x, )
- have no congruence as verbal complements
- go further from the head noun
Adjectives have a closer syntactical affinity to verbs, adjectoids to nouns; still, both have (partly separate) morphology for forming nouns and verbs; verbs more easily form adjectoids, nouns more easily adjectives.
Both classes have some exceptional derived forms among nouns and verbs. Some adjectives have synonymous adjectoids, but far from all. Prepositional phrases easily form adjectives as well, whereas pure nouns easily form adjectoids.
What word order this language otherwise would prefer depends a bit on what other syntactical features it has - I think something along the lines of det NOUN adjt. adjd. would be neat.