Glittery sparkle compliments and enhances your competitive skate (even more so if you're skating in a Showcase with spotlights). As in most performance art however, only a narrow range of use achieves the desired effect without appearing overdone. You should strive for an objective of "highlighting" -- rather than always being apparent, your sparkles should accentuate about a third of your moves.
I've seen three sorts of reflective devices: two types are sequins; the last is rhinestones. Rhinestones are small hard cut-glass crystal reflectors, faceted like a diamond with a metal backing. These glue onto your costume and if your dress doesn't already have enough you can purchase them at many craft and bead stores (or online even, see here and here).
The other two types of sparklies are small flat round pieces of plastic sequins with a tiny hole in the middle (to facilitate sewing onto the costume). One type is metallic and the other is semi-transparent plastic. You can buy these at most fabric stores (and some craft stores too).
Unless they're sparingly used and interspersed with the other two types, the reflective metallic sequins look cheap. I am sorry, they just remind me of store-bought Halloween costumes. The semi-transparent tonal plastic sequins are fine to use on a skating dress though.
Although rhinestones and tonal plastic sequins are both fashionable, they provide quite different visual effects. Crystal glass sparkles intensely as pinpoints of light at multiple angles. Xan tells me that a high-end dress for an elite skater can have 1500 rhinestones, which seems a bit excessive to me but okay, if you're going to be on TV then I say go for it (smile).
Otherwise a third of this quantity in strategic visual swaths is sufficient. Again artistic placement is paramount: if you evenly cover your dress with random crystals you won't get the same effect as if you lay them out visualizing how the eye catches your dress as it spins and angles.
Relative to rhinestones the plastic sequins are very inexpensive, and are usually sewn on by the thousands across large areas. The tonal flat sequins give one uniform sublimely gentle flash when hit at their reflective angle, but are otherwise nice as a gradual contrast shifter. As they have a different reflectivity from fabric they tend to make the covered swatch appear to vary in hue at different angles.
Although I have seen a couple nice dresses that made judicious use of both (in moderation) please avoid combining glass rhinestones and plastic sequins unless you're already an accomplished dress designer.
It's not particularly appropriate to use glass rhinestones on a man's costume (okay, maybe just a handful). Plastic tonal sequins are okay in understated moderation. Just my opinion again.
Skaters will try other modes of flashiness: glitter blush or eyeliner, sparkly hair pieces and hair gel. These may be fine if you're hoping for a camera close-up, but when you're on the ice we don't notice these from out here in the audience dear.
Finally although a sparkly dress is a nice highlight to your program, it shouldn't be the main draw. After all we really came here to watch how you skate.