As Hextall and Roseman will tell you, it's better to maintain some cap flexiblity because you never know what opportunities will present themselves down the road. If an international player in his 20s became available, then spending $20-25M a year on a 6 year deal is fine, because it's likely to be a good deal in 2021-22. Giving that kind of deal to a 30+ year old pitcher is madness, because he's likely to fall off the cliff by 2020 (look at Lee and Halladay).
It's not just whether you can afford it now, if you want to compete for the long haul, you have to stick to a consistent philosophy:
1) prioritize the farm system and player development, don't scrimp on personnel, facilities or signing prospects - I think we're in strong agreement here, I'd like to see them do a San Diego in the next year or two if they don't change the rules, spend $10-15M one year.
2) pay value, but don't get into bidding wars, because the guy paying the most is probably the dumbest guy in the room, don't be that guy ("winner's curse"). There are other players you can buy for more bang per dollar than the sexy FA that's getting overrated.
3) don't fall in love with your veterans, the reason for the farm system is to replace your over 30 players before their salary grossly exceeds their value - and use them to obtain more prospects. You need to retain a core group, based on both production and character (your core veterans set the tone in the clubhouse), but better to move a year early than a year late, which we've seen.
I have no problem with "strategic" overpays, but spending money because you have it I think poisons an organization, if throwing money is how you solve problems, then people stop being held accountable - and we saw that with the Phillies when they became a big revenue team - a lot of people were kept around far too long despite mediocre performance (see the farm system). Money was able to paper over organizational rot for almost a decade.
