Dell uses the Ultrasharp word for displays which have one or more of these attributes brighter, better color reproduction, higher resolution, better viewing angles.
For Laptop screens, Ultrasharp directly means higher brightness and resolution.
For Desktop screens this usually means higher brightness, color reproduction and better viewing angles.
Yes, the Ultrasharp sure are better than the economy models, the economy models usually use cheaper TN Panels while the ultrasharp models use better panels like S-IPS, S-PVA etc
But whether they are worth the money are not depends on your eyes. Some people cannot see the difference unless both displays are kept side to side, other like can see the difference directly. So Look for youself and choose.