Wow. Interesting dilemma. For me it is easier to look at the facts first.
1) Going to visit a friend for the weekend does not sound too extravagant and her initial reaction was to say "Sounds great." 2) Your finances are tight and you have agreed that because you have not dealt with finances well in the past so your wife has been "forced" to manage the money 3) Being the manager of finances is a VERY stressful position. 4) She admitted that she feels taken advantage of – It is a legitimate FEELING even if it is NOT exactly true. 5) You are not selfish. 6) Since this is a completely optional trip (No friend or family member in need and no family event), I think couples SHOULD make these decisions together.
Yes I see your wife's reaction as extreme but I also do not think it came out of nowhere either. I see her reaction as a sign that finances are wearing on her heavily.
This is so much bigger than a trip to Tucson. (By the way I love that city. Being able to see the mountains and the hiking in the foothills!) If I were you, I wouldn't make a decision one way or the other about Tucson right now. I would use this latest argument as a reason to get into marriage/financial counseling. You two need an objective outsider to help mediate those issues. Which come to think about it might be the way to spend that "extra" money??
So back to the immediate issue. Focusing on making your needs a priority does not necessarily need to include spending extra money on yourself, right? Yes this is a great opportunity but it is hitting a raw nerve with the financial issues. I do not think you can discount this part of the issue. The calling you selfish and complaining of feeling taken advantage of are emotional responses which are more complicated. I would not even bother with the selfish issue. You are not. The taken advantage of feeling is more interesting especially since you see that there might be some reason for that feeling.
Of course she could be having a similar Ms. Nice guy feeling: "I do all this work of making plenty of money, taking care of finances, helping pay for his kids and their college and when he finally gets some extra money, he does not even think of me." In your case, you think sex as THE reward but she might have her own reward in mind (a gift, a night away from home TOGETHER, a nice dinner out, etc.)
Questions for INFORMATION: Who makes the most money in your household? Who works the most hours? What percentage of the time do your kids from your first marriage spend with you? What things does your wife do daily or weekly for relaxation and enjoyment? What do you do daily or weekly?
But what is happiness except the simple harmony between a man and the life he leads? ~Albert Camus