Would it be prudent to wait till arrival from our overseas flight to purchase our train tickets or would an online ticket bought in advance be honored for any train departure if our flight arrival is delayed?
Well, if you will wait with ticket purchase till your arrival to Madrid, then almost certainly you'll end up paying full standard fare which is 89,4 EUR one way (or 143,05 in case you purchase return ticket) or at best so called Tariff Mesa (Group) ticket (71,5 EUR per person in case of 2 passengers or less if >2). Standard fare tickets can be exchanges, but basically it's useless to buy them online in advance, because on spot it will the same price. While discounted tickets (=real goal and reason to buy in online some time in advance) with RENFE (Spanish Railways) differ, ticket under offer "WEB" (up to 70% discount) cannot be exchanged at all, while those under offer "Estrella" can be (though for a fee 15%/20% -
http://www.renfe.com/EN/viajeros/tarifas/tarifa_estrella.html). So it is rather tricky choice for you, because from one side you can buy really cheap unchangeable tickets (WEB), from the other you can buy slightly more expensive (Estrella), but exchangeable discounted ticket and finally you can forget about in advance purchase at all, thus rely on standard/Group tariff tickets bought already when you in Spain.
Obviously choice is yours, we only can add that in cases like yours (with arrival by plane and potential delay) people sometimes simply book discounted tickets with a good margin of time. As result if the flight is on time you can just spend those few hours in Madrid, if flight is late, then you'll have a reasonable margin of extra time to make it to your connection.
I had just seen mention of a Spanish Pass for 163 E that would allow 4 trips and wonder if this would be a good choice as we need to go to and from Madrid -Malaga and might enjoy a day trip to Cordoba , Seville or some other city as well ..It would seem just Malaga -Madrid would be about 140 E round trip from fare postings I have seen. would that plan make sense?
Problem here is that tickets like Malaga-Cordoba or Malaga-Seville, even full standard fare, isn't very expensive (especially if to consider addition return discount), for instance one-way till Cordoba it's 26 EUR (except AVE trains), Seville is 23 EUR when using Media Distancia trains. So if to consider purchase of discounted tickets for legs Madrid-Malaga-Madrid and in addition even full fare Malaga-Cordoba/Seville-Malaga, then such combination will give you a better deal than Spanish Pass
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