Ditto what Tone said.
I understand what you mean by the uneven aging, but it's just that, aging. The only real way to take care of a matte finish is to keep it well cleaned. Believe it or not, adding polishes and silicones to matte finishes is bad and will help it age faster. Matte paint needs to breathe. By coating it, you are keeping oxidants in tghe finish and these oxidants slowly expand and can cause cracking, crows feet, and the discoloration. The discoloration (areas will seem lighter and darker, giving a zebra look) is actually where some some areas were able to breathe better than others.
In all, matte finishes are totally a thing of the past and ISUZU used it anyways. Their intentions were good, but the care as to how it aged was not. Hate to say it, but if its discolored or cracked, your best bet is to get it refinished. All polishing will do at this point is speed up the breakdown of the finish.
Sorry, more tech talk from an old automobile painter. 
Gary Noonan
'01 S/C VX / '18 Forester XT
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