Just take a look at some other leadership upgrades on new helmets or capes, and compare those to the increase for that belt offer.
You will notice that the increase on capes or helmets is much higher, and even the leadershipIncrease/costForItem will mostly be higher. At least that is what I have observed in the past.
I generally only buy new leadership items if the increase is at least 500 or so over the old item.
Thus, I bought no new belt or ring for about 30-35 levels from somewhere in the 50s to lvl 85 and just kept the old items until I finally got some offers with almost 500 increase.
Rest assured, the higher you get, the better rings/belts get, so better offers with bigger increase over your current one will come again.