I'm sure this has been said already, but I am too lazy to read all the posts.
Case #1 Yes, it is a better financial decision to buy whatever you want the first time. In the case of custom IEMs costing over a grand (if money is no concern then this does not apply but for most of us...), assuming you know what sound signature you think you may like, you may luck out and be absolutely thrilled with your new purchase. However, lets say your initial assumption was just slightly misguided. Now you have two $500 pieces of plastic which have no monetary value (you may be able to sell the cord) that have to be replaced. However, now that you have a good fitting custom (we will say that you went through the process to get it just right, which took 3 tries and many hours) you will likely have a hard time going back to universal unless you happen to be a lucky one with the standard ear and find the perfect tip (more hours and $$$). So now, instead of spending $1000 and getting it over with, you have just spent $1500-2500 to get it right and have endured a substantial amount of headaches.
Case #2 Lets go the other way and work our way up. This analysis is based on the normal progression of music in modern young people's lives assuming that they almost exclusively have always listened to portable gear and have no real experience with high end speakers and audio gear. Lets say you start with your free ibuds that came with your player. You realize they sound terrible and go and spend $75 at your local best buy for a low end IEM. For a while that sounds great so no headaches and no time wasted. A few months pass and you learn about audio compression and file types so you rerip your collection to flac and want to try a better IEM to see if you can realize the difference. You now do some research and find a good $150-200 IEM such as the ER4P or Sleek SA6. Again, the sound is better, the source is better so you are happy and have not wasted any time. So far you have spent $225-275. A few more months, maybe a year pass and you are now addicted. You now have an idea of what is meant my soundstage and understand what type of listener you are. You know what qualities you want in an IEM. Now you either buy an amp or upgrade to your dream custom IEM. It is now a few years later and new models have been released so you have purchased a better IEM than you would have 2-3 years ago when you though 128mp3 sounded just fine. So you now go out and spend $1200 for your new IEM which turn out to be just what you expected. You have now spent <$1500 and have exactly what you want and a solid knowledge base to support your decision and future purchases. You have constantly experienced better sound throughout the journey so you have not experienced any setbacks, headaches, or lost time like in case #1.
Personally, I believe Case #2 gives you the better education so you know why those $1000 IEMs sound better than the $.25 ones you just threw away and are not just relying on marketing slogans. It will also on average cost less as almost no one gets it just right the first time. However, if you have an extensive knowledge base and know what type of sound signature you like, then you will benefit from Case #1; however, if you are in that case, then you would not be asking for advice and would probably be the one giving it or even being paid for it.