The important distinction here is between cards and spells. Splice adds an effect to a SPELL.
Suspend exiles a CARD. A spell is what we call cards when they are on the stack, and no other time. If they're on the board, we call them permanents, and everywhere else, they're cards. So, you added the effect to the spell, but Gandalf exiles the card, not the spell. The spliced effect doesn't exist on the card. The card still says the exact same thing it always has.
So, you cast spell A, reveal card B to splice on the effects of spell B. Then you get both effects and
suspend card A. Over a few turns you remove some time counters, and cast spell A. You could, at that point, splice the effects of spell B onto the newly cast spell A, but you'd still have to pay the appropriate costs, otherwise you just get spell A's effects.