Well, it all depends on how optimistic you are and how you rate Dortmund's competitiveness at the moment. To me, BVB is "only" a rising star trying to get a foot in the door, with a focus on long term development. They could avoid the big bargain-sale despite the low wage structure up to this point mostly because of their stubbornness and very specific club culture, but there's no guarentee they might be able to do it in the future as well without this deal, so I see it as a necessary cash infusion. From here on out, BVB's first step is to get themselves into a position where they can compete with other elite clubs concerning the wages, being able to bind players with economic power alone. Maybe in the future, they'll be able to comepete for 'made' players as well. What they're trying to do is similar to what Bayern did before, only in fast-forward (and thus more risky)
What's more important though, the actual 'meat' of the decision is the change in the association articles and the subsequent capital increase measures to lure investors. BVB issued out 6 million shares to Evonik, equalling roughly 9 % of the shares. The current plan is to issue out another 24 million shares in the following years spread over 2 - 3 other investors, which at the current rate of the shares equals another 100 mil €. Since this is done via capital increase, it also means every capital increase decreases the overall share of the other investors who then have to buy more shares to keep their overall share, which should bring in another million or two, figuratively speaking. In order to lure investors, BVB can surely capitalize from the increased exposure in the US from next season forward. Once the investors are on board and the "brand" has been established, other possibilities rise as well which should ensure a steady economic growth.