<<"I've seen the excel file to help decide which kind of rail pass to buy. I
don't think I have the time now to put all those details though. I'm
thinking, since we are staying more than 3 weeks, would it be safe to
just buy both Swiss Rail Pass and Half Fare? Because 15 days is the max
for Swiss Pass and Half Fare is still cheaper than another Swiss Rail
Pass for fewer days. What do you think?">>
I have NOT done the math. So. I'm guessing.
I looks like you would need that "extra" pass for enough time and long journeys that you'd get you value out of the half fare card. But, you'll still be spending for each journey. And, you'll have "incidental" expenses in the city transport. A second Swiss Travel Pass could well pay off if you get one for a shorter duration.
I like to travel with a half-fare card- it fits my pattern. But, your last days have enough travel that I'm guessing ...repeat guessing...the STP still might pay off. Where it gets difficult is figuring out what would work best for the mountain transport in the Jungfrau region, where you will need to pay for cable cars, etc., during the whole trip.
That pattern on some of those is that the half-fare card is valid and the STP is not ( for full fare or at all) , but I can't offer enough detail to guide a decision. What is involved is that - even with an STP - some mountain transport would be cheaper with a half-fare card. But, this year, some of the bigger trips seem to accept (free) the STP when they did not before. Schilthorn, if I recall correctly.
I hope some one who is closer to those details can jump in here. The combination that you suggest would almost surely be cost effective. Also, with that combination, it might work best to start up the STP partway though your trip. But, I don't think so...you get benefit from the STP around Luzern.
Sorry I can't be more precise. It is alot of work to figure it out, The STP has extra value in that you can add trips that you had not pre-planned, and they cost nothing more. Except for some mountain transport. ;-(