Despite the fact that Siberia had been 'conquered' by the Russian Empire, it largely remained a borderland of the empire and I would argue remained so until the late 19th C. Siberia was sparsely settled and whatever Imperial presence existed was largely military in nature. Yet Siberia and the Russian Steppe provide incredible examples of the Russian Empire's information gathering expeditions about these borderlands with the express purpose of colonizing these lands that were largely unfamiliar (climatically) to many Russians.
While the conquest of Siberia dates to the 16th C., control and administration of these provinces was incredibly different and more difficult. Following Russia's conquest these unknown borderlands (Siberia being one of them, the Steppe the other key one) began to become the subject of rudimentary scientific expeditions to better understand these regions. They were primarily military expeditions and the establishment of Russian forts was a primary objective but the teams also included geographers, and botanists, etc. These efforts formed the beginnings of Russia's almost scholarly attempts to colonize and maximize the gain from their borderlands. Here the book The Plough that Broke the Steppes by David Moon is key, and in my humble opinion largely undervalued as a tool for Imperial Russian History. It is an incredible examination about the scientific innovation and discovery that accompanied Russian attempts to understand/colonize a foreign environment and how it went from being completely alien and foreign to a known unknown and then even to a landscape Russian farmers and peasants could control. Imperial data and knowledge allowed people to spread into these borderlands more successfully. To the early explorers of both the Steppes and Siberia the contrast to Central Russia with its forests could not be clearer.^1 Early settlers in Siberia were largely inefficient, Russian peasants could not adjust to the hostile environment and agricultural techniques that were so successful back in Central Russia were a failure.
Anyway these initial expeditions did little to entice Russia to push for large scale colonization, and to the inheritors of this early scientific legacy the reports and information gathered seemed woefully incomplete. In the 1830s as the Russian General Staff expanded and the founding of the Imperial Russian Geographical Society (famously the core institution for the so-called enlightened bureaucrats, who prioritized scientific study and data collection) marks the professionalization of this scholarly or scientific movement of colonialism. Late expeditions show Siberia to be a land of promise, Kazakhstan is portrayed as the second 'breadbasket' of the Empire, the Amur River is likened to the Mississippi in America. All of this is further pushed by the agrarian crisis in Russia's Black Earth region and is one of the main drivers that helps push Russia towards state sponsored peasant migration to Siberia. They see Siberia as a solution to a key problem the Russian Empire is facing as internal tensions are rising following monumental changes like the abolition of serfdom and increased urbanization. Stolypin's idea of "wager on the strong and sober" is key here, the idea being that people who have land to work (and there was plenty of land available in Siberia) would not be revolutionaries.
To sum up (as I have had a bit of wine while writing this/getting my notes and thoughts together) Imperial Russia knew little of Siberia at the time of conquest. It took generations of Imperial Scholars honing their craft to allow for the successful colonization of Russia's borderlands which Siberia included. Yet Russia's true interest in expansion into Siberia was largely political, it was seen as a solution to internal troubles as well as a land of untapped opportunity unlocked by this new wave of Imperial Knowledge.
Sources:
The Plough the Broke the Steppes by David Moon. (Seriously check it out, its environmental history at its best)
The Great Siberian Migration: Government and Peasant Resettlement from Emancipation to the First World War by Donald Treadgold.
In the Vanguard of Reform: Russia's Enlightened Bureaucrats, 1825-1861 by Bruce Lincoln.
Additional question: What was the climate in Siberia like back then? As cold as it is now?
I ask because it might be of influence on expansion plans.