It is quite true that the evidence that can be gathered from George Elliott's Silas Marner may point that it is both greed and loneliness what drives Silas's compulsive hiding of gold in his cottage. However, when his greed and loneliness are compared, it is safe to say that Silas's loneliness far outweighs his greed. Moreover, the evidence shows that it may be his loneliness that drives his obsessive behavior. Hence, Silas's behavior could have been manifested in any other kind of eccentricity: either saving up gold, or doing something else.
Silas was once a happy man and a productive member of society in his beloved town of Lantern Yard. He was about to be married, and he had trust in those around him. The betrayal of his friend, who viciously accused Silas of stealing and also stole Silas's fiancee, caused the reputation of Silas to come crumbling down. As a result, poor Silas Marner had to leave Lantern Yard in utmost despair.
This being said, nothing in Silas's life in Lantern Yard shows any indication of the odd behaviors that he displays in Raveloe. Nor does it show that Silas was ever prone to be financially ambitious or a hoarder of gold like he is in Raveloe. The problem with Silas is that the impact of the betrayal left such a negative dent in his psyche that he has had to figure out a way to be in control of "something". This is why weaving is his conduit to forget about the world: because he can control and master every step of the weaving process.
Similarly, hoarding becomes another eccentric way for Silas to regain the inner power that was sucked away from him in such a cruel way by the people whom he trusted in his former town. Since he feels that money is power, he gathers all of the gold that he can. Yet, there is hardly a really good reason why Silas would want all of that money in his hands. Sure, he has plans with it, but it seems more that Silas is overcompensating his emotional losses with material things.
Therefore, while greed and the love for money are common tastes that color the human nature, Silas Marner's character is not meant to be shown as a mere money-hungry man, but a man who needs a dose of human connection. Money, in Silas Marner, or the loss of it, is the conduit through which Silas finally makes a much needed entrance into the real world that he so desperately tries to avoid.