Why do Baptists even baptize in water at all considering their "spirit baptism" views? It is common for Baptists to take the position that any passage in scripture that sounds like its saying baptism is required for salvation is referring to "Spirit baptism." [Examples, Acts 2:38, Gal 3:26-27...] 

If this is really their belief, why do they even administer the "ordinance" (their term) of "Water baptism" at all?  I mean if all references to baptism are really "spirit baptism" why even waste your time baptizing in water, and why make your beliefs about immersion and credo-baptism a distinctive to the point of calling yourself "Baptist" (and with a capital "B" to boot) if you don't think the baptism that is administered by men has any real relevance to salvation and that its only "spirit baptism" (which obviously can only be administered by God) that matters?

[Knowing my own perspective may help in formulating an answer I guess: I also believe in immersion and credo-baptism, and I believe that spirit baptism takes place in water baptism, never separate, neither before or after but always at the same time; the only exception being in Acts 10 when God diverged from the normative order to show Peter that Gentiles are acceptable candidates for baptism and not just Jews. Its possible, I suppose that Baptists mean the same thing(?) and so I guess knowing I believe this could help answer the question.]
Baptists practice baptism because it is something taught in Scripture.  

Your question hits exactly on the distinction between those denominations that believe that baptism is necessary for salvation, and those that don't. Baptists don't see it as necessary for salvation.  Instead, it's seen as an outward expression of obedience. 

The analogy is graduation.  getting your diploma doesn't impart knowledge onto you.  Getting an education - sitting through class, studying, etc. imparts knowledge.  Yet people participate in the graduation ceremony.  Similarly, Baptists, and other groups that believe that baptism is not a necessary component of salvation practice it as a celebration, or an outward expression of the fact that they are already saved, and have already been born again of the spirit.

Backing reference: Baptists: Believer’s Baptism 

Excerpt:


  Baptists believe that the Bible teaches that baptism is important but
  not necessary for salvation. For example, the thief on the cross (Luke
  23:39-43), Saul on the Damascus road (Acts 9:1-18) and the people
  gathered in Cornelius’ house (Acts 10:24-48) all experienced salvation
  without the necessity of baptism. In his sermon at Pentecost, Peter
  urged those who had repented and believed in Christ to be baptized,
  not that baptism was necessary for salvation but as a testimony that
  they had been saved (Acts 2:1-41).
  
  Thus, baptism is symbolic and not sacramental. Baptists believe that
  the Bible teaches that baptism symbolizes that a person has been saved
  and is not a means of salvation. Baptism is not a means of channeling
  saving grace but rather is a way of testifying that saving grace has
  been experienced. It does not wash away sin but symbolizes the
  forgiveness of sin through faith in Christ.
  
  While baptism is not essential for salvation, it is a very important
  requirement for obedience to the Lord. Christ commanded his disciples
  to baptize (Matthew 28:19) and therefore baptism is a form of
  obedience to Jesus as Lord. Baptism is one way that a person declares,
  “Jesus is Lord.”