The Riverdale section of the Bronx, including Fieldston, Hudson Hill, North Riverdale and Spuyten Duyvil, enjoyed price growth over the past year along with more sales activity. Median sales price increased 7.5% to $280,500 from the year-ago quarter. Average sales price followed the same pattern edging up 2.7% to $389,520 over the same period. The number of sales expanded 10.3% to 172 while inventory slipped 2.7% to 257 respectively from the year-ago quarter…