I think advice like this is often over-generalized and applies more when an ambitious improving player has his sights on scalping titled players one day and perhaps getting said title as well.
For a shy, passive D-Class player who needs to learn to go for the jugular on each move, I'd think a healthy dose of gambit play would do wonders until he/she learns to dole out moves based on initiative and aggression. For somebody who already has this quality in droves, gambit play may not help so much.
I played nothing but Gambits till USCF 1500-1600 and soon realized how they were helping me win isolated games but had me returning home from a weekend tourney with a score no more than 2 or 3 out of 5. Really strong opponents would tear me apart so it almost seemed like the surprise/psychological value was diminishing as I faced stronger opposition.
I did get lucky a few times beating a top dog player at our club events, but he booked up all the busts and each time I played him again, I was essentially starting every game with a disadvantage ( with said gambit) which he capitalized on from the get-go.
I pretty much was at a crossroads where I had to ask "What is fun for me?"
Going to the clubs and weekend tourneys, beating other 1500-1600s with these openings and scalping a few titled players on bullet/blitz BUT not standing a chance of surprising a really strong player OTB with these systems. Sure, I'll lose a lot more than I win in open tourneys, but I'll get an awesome attacking combo once in a while. Was this the last stop on my "chess is fun" bus?
OR
beating stronger/1800+ players more consistently and not getting outplayed in an opening whenever I faced them OTB. Or better yet, being able to organically grow and nurture an opening repertoire that had tons of sound theory to back it up ... best of all => not having to "re-learn" or uproot any opening system because it suddenly stopped becoming useful for the rating class I was competing against. Realizing that tactics, speculative sacrifices and combos are not the only fun thing about chess.
So that was a no brainer to me. => so I upgraded most of my repertoire and it has been helping. I get to actually go over more published annotated Master games in the sound-er openings than I ever did with the gambit lines as well. My coach helped me pick out sounder-versions of openings from the kind of open tactical positions I used to play with Gambits.
For example =>
Gave up the Danish, picked up the Scotch.
Gave up the Morra, picked up the Alapin.
I *do* regret not doing this earlier on.
read the following I know he is a GM and he may be right on many things, but do you think he is entirely right on this one? Personally I think you can learn a lot playing gambits.
GM Lars Bo Hansen writes in his book "how chess games are won and lost"
"I often see players at clublevel play:
Blackmar-Diemer Gamibt, Latvian Gambit, Elephant Gambit, Morra Gambit, Wing Gambit or Owens defence
even among rather strong players. while these opening may lead to short term result due to the surprise effect -I believe building an opening repertoire on such opening is harmful for the prospects of improving in the long run. I only have one advice for ambitious players: drop such opening from your opening repertoire before it's to late"