I was a regular on trains for quite an extended period of time (alas no more), sometimes I was in Dublin a lot and it was better value to get a season ticket but I bought plenty of daily point to points too. It has been ticket to Connolly since 2015 at the very least I think because I recall querying it about then when I was told that it wasn't valid for my journey to Stephen's Green, they let me away with it but I had never actually been challenged on it before that.
Irrespective, my point stands, you're better off getting a Leap card. If by "Kildare" you mean Sallins & Naas or Hazelhatch & Celbridge you can use the Leapcard from that station which would also mean you would get the benefit of the daily cap of €7.60. If you mean Kildare/Monasterevin/Athy you'll still need to get the point to point ticket but get it to Heuston and use the Leap from there.
I changed over to cycling or walking from Heuston. I never bothered trying to get a bike at Heuston though, head up the hill to James' St and cycle from there, quieter route than the quays.