I assume you are speaking about Spanish Civil War Kar.98a and wz.29's? The distinction is important because generally Spanish imports are less valuable than normal rifles from other sources.
The Polish rifles sold to Spain were bought by the the "republican" forces (far left socialists, "intellectuals", reds-communists, unions, atheists etc.. basically Spain's version of the Popular Front in France), ostensibly the "government" or loyalist forces, who highjacked the government (period articles exist that list the numerous discrepancies in the then current government legitimacy). These rifles were bought with Spain's gold reserves from Poland, because there was a League mandated embargo (and probably considerable embarrassment for the Poles to deal with communists, - ideologically the Poles were opposed to the Spanish "republican" government, but gold/hard currency has a way of lessening hostility) the rifles were scrubbed of their markings. This scrubbing considerably reduces the value of these rifles.
The German rifles sent to the Nationalists (Franco) were not scrubbed generally, so they retain some value, but most were subsequently altered by reworks and more importantly by importers.
In short, you need to judge a rifle from Spain, or any other rifle, by the characteristics of the rifle, its originality, its condition, which means that most Spanish imports will have limited collectors value to German rifle collectors. Naturally collectors that focus on the Spanish Civil War, a very interesting campaign of its own, will find merit in the rifles that have features that reflect the period (naturally many of the rifles imported into the US since the 1960's will be seriously compromised for them as well..)
I think for most German rifle collectors, most Spanish Civil War rifles will have limited appeal, for our purposes here the Polish rifles that were scrubbed will have very little appeal. Which is a shame because Polish marked rifles in fine condition can be worth more than German rifles in the same condition. They have a strong following.