I think a comment on Ex 25 is most appropriate. I can think of at least three comments that could be made:
1. Contributions were asked for by God, but not demanded... it was to be from everyone whose heart moved him. Today, we also ask for voluntary contributions to promote the worldwide work in all its facets, but it is never demanded of anyone. We never demand funds, pass around collection plates or anything like that. It is always "from everone whose heart" moves them.
2. Contributions taken were to accomplish a specific purpose, the one-time building of the tent, tabernacle and the ark of the convenant. Likewise today, when a specific need arises, we may have funds set aside for that one-time need, such as a major repair on a kingdom hall project, the building of an assembly hall or something like that. Once the need is done, the brothers and sisters are not continually burdened with additional contributions that go beyond that specific need.
3. In the days of the Israelites, Jehovah had his tabernacle and tent and that was the central place where Jehovah dwelled in spirit. Today, however, the situation is different. As Acts 7:48 says, "The Most High does not dwell in houses made with hands." This being the case, we could not imagine Jehovah today asking for contributions to be taken to build a building for him. True, we have Kingdom Halls, Assembly Halls and branches, and these are built using voluntary donations "from the heart". But we would never take up a specific contribution to expand these contributions beyond what we voluntarily give on a personal basis.