The terms 'nabobs, gold mohrs and palaquins' I believe are associated with officials in service in India.
Possibly, with this line JA suggests Colonel Brandon served in the army in British India and amassed some fortune.
On his return, he may've used the capital to pay off debts and invested in his family estate. By this time, Brandon's prudent control has probably brought the estate back to prosperity.

I think Robbin has a good point people are often jealous of those to whom they feel inferior. In Ch. 15 Willoughby calls himself 'a dependent cousin' by contrast, Brandon is independent, a self-made man whom Willoughby considers to have 'more money than he can spend'.
His comment Brandon 'has everybody's good word and nobody's notice' is outstandingly untrue-
Willoughby would realize Col. Brandon is well regarded by local society figures Sir John and Lady M who continually invite him to Barton.
Right in front of him, Elinor speaks up for Brandon, 'I can only pronounce him to be a sensible man, well-bred, well-informed, of gentle address, and, I believe, possessing an amiable heart.' (ch.10)
Yet Willoughby stubbornly dismisses Elinor's words, he becomes abit sarcastic, he can't stand Brandon highly spoken of.
His stirring Marieanne to a contempt with little reason, I think, reveals him giving vent to his dislike and jealousy of Brandon, and indicates Willoughby makes little attempt to control his worst impulses.

Perhaps Willoughby realizes apart from Sir John's calling him 'a decent shot'... nobody thinks so highly of him. I mean who'd really miss Willoughby when he's not around ? ;)