Both these conditional sentences are grammatical:
If I bought that apartment, we'd have a place to party whenever we wish.
If I bought that apartment, we'd have a place to party whenever we wished.
Is there a slight difference in meaning between wish and wished though? Does the preterite form signal a reduced likelihood? Or does it simply comply to the overall "past tense" of the apodosis?
It really depends on what you mean. If you're talking about something that is unlikely or impossible to happen in the present or future, then the second condional sentence is what you want.
eg. If I bought that apartment, we would have a place to party whenever we wished.
Remember that "wished" here, is unreal past (refers to the present and future).
If you are likely to buy the apartment , use the first conditional form:
eg. If I buy that apartment, we will have a place to party whenever we wish.
Would say wished to because it sounds as though it were a concealed second conditional: we could have a party whenever we wanted to
If we wanted to have a party, we could have one.
However I would stick to wish if the introductory part were a first conditional If I buy this apartment we will have a place to party whenever we wish to
Note I have used wish(ed) to as in want to
In common spoken English, there doesn't seem to exist any significant difference between the two tenses, at least descriptively. However, emphatically the second sentence gives me the impression that the events took place further back in time. This can be implied even further by adding "we'd have had a place...", though this is subjective to the writer/speaker. Contrarily, as a native English speaker I take the first sentence to be spoken in present tense. Informally, "If I bought..." can be used in the present tense for something taking place currently, though this is not prescriptive grammar.
