Shiny Pokemon do not impact the strength of the Pokemon in any Pokemon game and exist mainly as collectibles-- It's up to you yourself if they're worth it or not. However, Lucky Pokemon reduce the amount of Stardust needed to power up it's CP. Rhypherior's strength relies on your trainer level, it's stats, and cp, not on if it's shiny or not.
To view your Pokemon's stats, press "Appraise" while viewing the Pokemon.
If you'd like to power it up more with less stardust, Lucky is the way to go.
Hope this helps!
source: experience
