Both NTO and NXG were mostly base metal plays unlike EXK, and, in any case, EXK could looks more similar to NXG rather than NTO, because it has mining operations.
Also, talk about similarities must include a bold assumption that bull market in metals is already on the way as it was in 2004. This assumption looks shaky because of Chinese factor. It was mostly Chinese growth that fueled strong metal prices in 2003-2008. At present juncture, Chinese growth changed to Chinese crisis.
Silver presents a minuscule sector of global economy. One can hardly find any big market player caring about silver price. For example, US government or Fed Reserve do not care about it; they care about US economy (it is mostly Fed Reserve). Sometimes, gold and silver price suffer collateral damage in this process. In any case, no "manipulations" can be responsible for it. It is better for investment purposes to identify and assess the process (Fed policies), whether it is successful or not. The accuracy of this forecast would be extremely important for every investor.
In general, streaming companies provide money to miners in conditional way; it is usually called a "deposit" and it is considered a debt, secured by miner's assets. Once a miner gets to production, it starts making payments to a streaming company; these payments reduce amount of the deposit. If a mining company goes under then remaining part of the deposit constitutes a monetary claim on miner's assets.
If I remember Mt.Milligan streaming deal conditions correctly, then it was exactly a story of "deposit". Please, note that I didn't look at that deal details for many years, since the deal was announced. It was made in a very different market.