I personally love beautiful and functional buildings. But beauty is not necessarily equivalent to extravagance. A humble building can still be an object of beauty.
I love it when members come together and decide to put up a beautiful place of worship. In many communities, it probably is the only beautiful landmark the locals can access without restriction or discrimination. It is inspiring (especially to children) and has a significant spiritual benefit in that it teaches people about sacrifice.
Building a beautiful church does not necessarily mean that the church cuts down on mission budget and activities. Effective mission, in my opinion, is ministering to the needs of those in the immediate vicinity. If I may borrow from the words of Jesus, sacrificing to erect the church is good and all, but we should not forget weightier matters of justice (Mathew 23:23). In the Adventist church, there was always a provision for communal amenities, especially a community school, a medical facility or both (Read Evangelism 375 - 381).
My main issue is when the project is driven from the top. In such a case, it tends to serve vested interests. Members are unrealistically overburdened with endless contributions that make them detest the very worship service. In the end, it is a zero-sum game to the detriment of the church members. Obsession with erecting extravagant edifices, with every church competing to beat the next, with no significant impact to the community (local community and the community of believers) is detestable in my opinion. Those who drive this agenda often guilt trip members with, "Solomon built a magnificent temple for the Lord." The reality is that Solomon was the King of Israel, with access to endless wealth - both inherited from his father and those generated during his tenure. All Israel was involved in building the temple. And it was only one temple they built with all these provisions.