Does it actually SAY that Heaven will be joyous in The Bible? ...and, come to that, does it actually state, beyond doubt (or a different interpretation) that the joy there is far, far beyond that we can experience in this world or even imagine?

BEFORE anyone points to the Corintheans "Eye hath not seen..." it must be pointed out that that is followed by an explanation that, despite the fact we couldn't have guessed for ourselves, God has revealed it to us.

Despite God having revealed it, I'm seeming to find that all the things people had excited me about Heaven with seems to have been 'added on' as good guesses. Current joys are mere sunbeams of that to come? All joys will be ressurected as impossibly greater than they were now?
The Bible does not say there will be infinite joy, but rather the absence of its opposite.  Revelation 21:4 states:


  4 He will wipe away every tear from their eyes, and death shall be no more, neither shall there be mourning, nor crying, nor pain anymore, for the former things have passed away.”


The absence of death (cf. 1 Corinthians 15) and the absence of tears seems to indicate an abundance of joy.  It isn't explicit, but it is pretty easy to extrapolate to that position.