It really depends on your system. Garbage in, garbage out; but the law of diminishing returns plays into DAC's. You have to determine if the diffrence is worth the price.
I'm not familiar with your dvd player, but speaking from experience dvd players have excellent cd sound quality. As far as the player only costing $140, I have a sub $100 portable player that sounds better then a 8+ year old cd player that cost several hundred dollars. Great sound quality does not have to be expensive, and advances in technology have made excellent performance the norm.
If you want the difinitive answer as to whether a cd upgrade will sound better to you, then visit a local hifi audio shop. Any good dealer would allow you to audition a quality cd player at home.