rocketing
pp. Spending a great deal of money on a few important items while spending only an average amount or less on everything else.
Examples
2007
Brand Pretorius, chairman of McCarthy Motor Holdings, concurs: "Motor industry analysts have identified a trend called 'rocketing'. In terms of this trend, when black buyers migrate from lower to middle and higher income groups, they tend to spend their money on products and services that demonstrate that they have arrived," he explains….

Interestingly, some of these buyers spend little on less visible items — such as insurance, health cover and, in some cases, housing.
—“Black Diamonds shine bright,” Cape Times (South Africa), November 15, 2007
2003
In other words, they shop the way most Americans shop, in that confused hierarchy-busting manner the market researchers now call rocketing. They spend lots of money on a few items they really care about — their barbecue grills or their lawnmowers — and then they go downmarket to Wal-Mart to buy most of the other stuff they don't care about. This isn't upper-class consumption or even relentlessly middle-class consumption. It's mixed-up no-class consumption.
—David Brooks, “A Nation of Grinders,” The New York Times, June 29, 2003
2002 (earliest)
Consumers are spending a disproportionate amount of income in certain categories, like things automotive, according to a recent survey conducted by the Boston Consulting Group. It's called ''rocketing,'' says researcher John Butman, and he says the shaky economy is not making a drastic dent in this category of spending.

''Rocketing is occurring at every income level,'' Butman says. ''When people are feeling fear or worry about the economy, they find solace in goods that give them pleasure.''
—Tamara Warren, “Driving downmarket,” AutoWeek, December 16, 2002