I think pulling for a specific unit can be the most depressing thing, wether you invest money or not. If you get that unit, or better if you get that unit very soon, or right away at first pull, it can be very satisfying. On the other hand, if you spend all your hard earned orbs and dont get the unit you wanted most it can be very depressing. When you have to resort to buying orbs and still dont get that unit can be devastating.
IMO FE Heroes is played best with little to no expectations of what to get from a pull as you dont really have any influence on what you get, only chances. Even if you spend money, you are just paying for more chances. I made that mistake in the past when the IKE banner was up, after spending all my orbs and still not getting him I bought orbs and once I finally got him it didnt feel very rewarding to me.