A lot of collectors will tell you that catalog prices are "ridiculously high", but I don't agree. Scott prices are for "very fine" stamps, and 80%+ of stamps are lower quality than that. Scott prices for cheap (<$10) stamps are usually very high in my experience - the less expensive, the higher the difference in catalog vs market price. The minimum is 25c, and nearly every stamp at the minimum is worth less.
Also, scott prices are full retail prices for a single stamp - no accounting for volume of, say, buying a year set. And definitely not what a lone collector will get from a dealer.
With all those caveats, I think scott catalog value is still on the high-end for most items. Look at actual dealer price lists and sold (not asking) prices on
ebay, and be sure to note the quality of the sold stamps. And note that a even a small fault will drastically reduce the price.